ICES Journal of Marine Science: Journal du Conseil

Govoni, J. J.; Hare, J. A.; Davenport, E. D.; Chen, M. H.; Marancik, K. E.

doi: 10.1093/icesjms/fsp269pmid: N/A

Govoni, J. J., Hare, J. A., Davenport, E. D., Chen, M. H., and Marancik, K. E. 2010. Mesoscale, cyclonic eddies as larval fish habitat along the southeast United States shelf: a Lagrangian description of the zooplankton community. ICES Journal of Marine Science, 67: 403411.The Charleston Gyre region is characterized by continuous series of cyclonic eddies that propagate northeastwards before decaying or coalescing with the Gulf Stream south of Cape Hatteras, NC, USA. Over 5 d, chlorophyll-a concentration, zooplankton displacement volume, and zooplankton composition and abundance changed as the eddy moved to the northeast. Surface chlorophyll-a concentration decreased, and zooplankton displacement remained unchanged as the eddy propagated. Zooplankton taxa known to be important dietary constituents of larval fish increased in concentration as the eddy propagated. The concurrent decrease in chlorophyll-a concentration and static zooplankton displacement volume can be explained by initial stimulation of chlorophyll-a concentration by upwelling and nutrient enrichment near the eddy core and to possible grazing as zooplankton with short generation times and large clutch sizes increased in concentration. The zooplankton community did not change significantly within the 5 d that the eddy was tracked, and there was no indication of succession. Mesoscale eddies of the region are dynamic habitats as eddies propagate northeastwards at varying speeds within monthly periods. The abundance of zooplankton important to the diets of larval fish indicates that the region can provide important pelagic nursery habitat for larval fish off the southeast coast of the United States. A month of feeding and growth is more than half the larval duration of most fish spawned over the continental shelf of the southeastern United States in winter.

Miethe, Tanja; Dytham, Calvin; Dieckmann, Ulf; Pitchford, Jonathan W.

doi: 10.1093/icesjms/fsp248pmid: N/A

Miethe, T., Dytham, C., Dieckmann, U., and Pitchford, J. W. 2010. Marine reserves and the evolutionary effects of fishing on size at maturation. ICES Journal of Marine Science, 67: 412425.Size-selective fishing may induce rapid evolutionary changes in life-history traits such as size at maturation. A major concern is that these changes will reduce population biomass and detrimentally affect yield and recruitment. Although marine reserves have been proposed as a tool for fisheries management, their evolutionary implications have as yet attracted little scrutiny. A simple model is used to investigate whether marine reserves can be expected to mitigate the evolutionary impacts of fishing on maturation size. The adaptive dynamics of size at maturation are analysed based on a stage-structured population model including size-selective fishing and marine reserves with different retention rates. As has been shown before, imposing greater fishing mortality on the largest individuals promotes an evolutionary change towards smaller maturation size. In the model, protecting part of a fish stock using a marine reserve can prevent such fisheries-induced evolution, and this protection critically depends on the type and extent of movement between the reserve and the fished area. Specifically, although the frequent movement of large adults increases catches of large adult fish outside a marine reserve, it also reduces the reserve's effectiveness in preventing fisheries-induced evolution. In contrast, when there is exchange between protected and fished areas through juvenile export alone, a marine reserve can effectively prevent evolution towards smaller maturation size, but does so at the expense of reducing the yield of large adult fish. Differences in the movement behaviour of successive life stages need to be considered for marine reserves, to help make fisheries more sustainable evolutionarily.

Libralato, Simone; Solidoro, Cosimo

doi: 10.1093/icesjms/fsp249pmid: N/A

Libralato, S., and Solidoro, C. 2010. Comparing methods for building trophic spectra of ecological data. ICES Journal of Marine Science, 67: 426434.The distribution of biomass, production, and catches over trophic levels (TLs) of the foodweb has been shown theoretically and empirically to provide powerful insights into ecosystem functioning and the effects of fishing. One approach for building trophic spectra of ecological data is based on smoothing original data and assuming zeroes when no values are available for a TL (smoothing-based method). An alternative method is proposed, based on the distribution of ecological data according to density functions (dispersion-based method), and a systematic review of the different alternatives is presented. Six different methods for building trophic spectra, i.e. the smoothing-based and five alternative forms for dispersion-based (using normal, lognormal, and Weibull distributions, also including shifted lognormal and Weibull with zero at TL 2), were applied to ecological properties (i.e. production, biomass, and catches) derived for 24 foodweb models to test their relative performance. The smoothing-based method suffers from the lack of consistency with original data and from unrealistic emergent properties, such as transfer efficiency. The analysis demonstrates the advantages of the dispersion-based method for overcoming these issues and shows, using transfer efficiencies estimated from the models (flow-based estimates) as a reference, that the normal density distribution function performs better.

Barrento, Sara; Marques, Antnio; Vaz-Pires, Paulo; Nunes, Maria Leonor

doi: 10.1093/icesjms/fsp268pmid: N/A

Barrento, S., Marques, A., Vaz-Pires, P., and Nunes, M. L. 2010. Live shipment of immersed crabs Cancer pagurus from England to Portugal and recovery in stocking tanks: stress parameter characterization. ICES Journal of Marine Science, 67: 435443.Cancer pagurus is commercially one of the most important crustaceans exploited in the UK and Ireland, but the main markets are in southern Europe, to where live edible crabs are transported. In this study, potential stressors during the live trade chain from England to Portugal were identified and related to changes in haemolymph parameters. Before their live transport, 60 crabs were tagged, their vigour was assessed, and their haemolymph was sampled; 30 crabs were placed in the bottom of a vivier-truck tank and the balance at the top (1 kg crab l1 in a total of 700 kg). The sampling procedure was repeated after immersed live transport (58 h), and during subsequent recovery (6, 24, 48, 72, and 96 h) in seawater at Portuguese storage facilities. Haemolymph parameters included pH, d-glucose, l-lactate, and haemocyanine. Cumulative mortalities at the end of the experiment (96 h in recovery tanks) of bottom and top crabs were 8.9 and 10.7, respectively. Vigour assessment predicted crab mortality well. The main stressors identified were poor handling; air exposure during unloading, and deficient transport conditions. d-Glucose and l-lactate increased during transport with acidification of the haemolymph. Concentration of l-lactate reached control levels after 24 h of recovery, but haemolymph remained acidic and hyperglycaemic even after 96 h. The transport conditions promoted anaerobiosis, so alternatives need to be considered.

Urquhart, Katy; Pert, Campbell C.; Fryer, Rob J.; Cook, Paul; Weir, Sarah; Kilburn, Rachel; McCarthy, Una; Simons, Judy; McBeath, Sonia J.; Matejusova, Iveta; Bricknell, Ian R.

doi: 10.1093/icesjms/fsp271

Grger, Joachim P.; Kruse, Gordon H.; Rohlf, Norbert

doi: 10.1093/icesjms/fsp259pmid: N/A

Grger, J. P., Kruse, G. H., and Rohlf, N. 2010. Slave to the rhythm: how large-scale climate cycles trigger herring (Clupea harengus) regeneration in the North Sea. ICES Journal of Marine Science, 67: 454465.Understanding the causes of variability in the recruitment of marine fish stocks has been the holy grail of fisheries scientists for more than 100 years. Currently, debate is ongoing about the functionality and performance of traditional stockrecruitment functions used during stock assessments. Additionally, the European Commission requires European fishery scientists to apply the ecosystem approach to fisheries in part by integrating environmental knowledge into stock assessments and forecasts. Motivated to understand better the recent years of reproductive failures of commercially valuable North Sea herring, we studied large-scale climate changes in the North Atlantic Ocean and their potential effects on stock regeneration. Applying traffic light plots and time-series (TS) analyses, it was possible not only to explain the most recent reproductive failures, but also to reconstruct the full TS of recruitment from climate cycles, indexed by the North Atlantic Oscillation and the Atlantic Multidecadal Oscillation. A prognostic model was developed to provide predictions of herring stock changes several years in advance, allowing recruitment forecasts to be incorporated easily into risk assessments and management strategy evaluations, to promote a sustainable herring fishery in the North Sea. Insights gained from the analysis permit reinterpretation of the sharp decline in the North Sea herring stocks in the 1970s.

Abascal, Francisco J.; Mejuto, Jaime; Quintans, Manuel; Ramos-Cartelle, Ana

doi: 10.1093/icesjms/fsp252pmid: N/A

Abstract Abascal, F. J., Mejuto, J., Quintans, M., and Ramos-Cartelle, A. 2010. Horizontal and vertical movements of swordfish in the Southeast Pacific. – ICES Journal of Marine Science, 67: 466–474. In all, 21 swordfish (Xiphias gladius) were tagged with pop-up archival satellite tags in the Southeast Pacific. Despite problems of premature release, the information obtained provided insight into the horizontal and vertical behaviour of the species in the area. A consistent migratory pattern was observed, fish moving northwest by autumn and presumably returning south by early spring. Swordfish typically forage in deep water during the day and stay in the mixed layer at night, although this behaviour is occasionally modified. The maximum depth recorded was 1136 m, and dives deeper than 900 m were found in five of the six tags analysed. There was a significant positive relationship between average depth by night and visible moon fraction. Introduction Swordfish (Xiphias gladius) are highly migratory and are found worldwide, but mainly from 45°N to 45°S, and are the most widely distributed species of billfish (Palko et al., 1981). In the Pacific Ocean, they are caught mainly by longline and driftnet by Far East and western nations. Although some assessments carried out in recent years seem to indicate that total and spawning biomass are above levels that would maintain maximum sustainable yield (MSY) in the Pacific Ocean (Hinton et al., 2005; Kolody et al., 2006), other indicators, such as average size or catch rates in certain areas and fisheries, together with model uncertainties, have raised concerns about fishery sustainability. Most assessment uncertainty is attributable to an absence of information on the biology of the species, such as on stock–recruitment relationships, mortality, age-at-first-maturity, and stock structure. Some studies have found little genetic differentiation along a U-shaped corridor in the Pacific Ocean (Reeb et al., 2000; Kasapidis et al., 2008), but others have suggested the possible existence of four separate stocks of swordfish, centred in the Northwest, Northeast, Southwest, and Southeast Pacific (Alvarado Bremer et al., 2006; Hinton and Alvarado Bremer, 2007). Aside from this, little is known about the spatial extent of the stocks, migration patterns, or mixing rates of swordfish. Over the past few years, the development of telemetry tagging techniques has provided a useful tool for the study of large pelagic fish. However, despite the economic importance of swordfish, little research has been conducted on its migratory patterns or habitat preferences. Carey and Robinson (1981) and Carey (1990) used acoustic tags to describe the diel vertical migration of swordfish, along with their horizontal movements in coastal waters. The main disadvantage of acoustic tags is that tracks tend to be short in duration and provide little information on migration patterns. Nevertheless, these studies have provided insight into feeding behaviour and swordfish association with topographic features. Pop-up satellite archival tags (PSATs) were first used on swordfish by Sedberry and Loefer (2001) in the West Atlantic. Interesting results were obtained, but these tags only recorded a small number of temperature measurements, without any estimates of light level or depth, and the deployment times were short. Recently, Neilson et al. (2009) described the migration patterns of swordfish in the Northwest Atlantic by pop-up tags. In the Pacific, there is little information on migratory patterns. Takahashi et al. (2003) tracked a single swordfish carrying an archival tag for more than 11 months and described a cyclic migration pattern off the east coast of Japan. Dewar and Polovina (2005) reported the preliminary results of a project that intended to deploy a total of 30 PSATs in swordfish off southern California, but at the time of their report, and because of the vertical movements of fish at dawn and dusk, they could not estimate geolocations from the archived light-level data. During the third regular session of the Scientific Committee of the Western and Central Pacific Fisheries Commission, Holdsworth et al. (2007) provided information on the horizontal movements of seven swordfish tagged in New Zealand waters, with deployments of 66–236 d, and showed consistent movement patterns among all the fish tracked. Current assessments of swordfish stocks carried out by different regional fisheries organizations incorporate information on stock structure deduced from pop-up tags. The aims of the current study are to contribute to the knowledge of swordfish movements and habitat preferences in the Pacific Ocean. Material and methods In all, 21 swordfish were tagged around Nazca Ridge (off northern Chile) during the period March–June 2007 using MK10 PSATs from Wildlife Computers. The tags were programmed to summarize depth and temperature data at intervals of 1–12 h, with deployment duration varying from 1 to 14 months. The tags include a failsafe mechanism to release from the fish for premature detachment, detected when the tag remained at a constant depth ±8 m for more than 72 h. Depth bins were 0, 10, 25, 50, 75, 100, 150, 200, 250, 300, 350, 400, 600, and >600 m, and temperature bins were 5, 10, 12, 14, 16, 17, 18, 19, 20, 22, 24, 26, 28, and >28°C. Swordfish were captured by two commercial longliners participating in a scientific project. Tags were attached by a monofilament leader to the dart, which was inserted into the dorsal musculature close to the first dorsal fin with the aid of a tagging pole once the fish was brought alongside the vessel. A swivel and a mechanical release device (RD1800, Wildlife Computers), which cuts the tether when depth exceeds 1800 m, were used. Two types of dart were assayed: stainless steel and medical-grade nylon (E. Prince and M. Musyl, pers. comm.). Only fish in prime condition and measuring >140 cm lower jaw fork length (LJFL), ca. 35 kg round weight, were tagged (mean 166±13 cm, range 140–220 cm). Satellite-transmitted information on depth, temperature, and light level was processed using Wildlife Computers software. Linear least-squares regression analyses were performed to test possible correlations between average depth at night and the phase of the moon. Data from visible moon fraction were obtained from the United States Naval Meteorology and Oceanography Command (www.usno.navy.mil) and arcsine-transformed before statistical analysis (Zar, 1996). Qualitative relationships between vertical habitat utilization and dissolved oxygen concentration, extracted from the World Ocean Atlas (García et al., 2006), were also explored. For track estimation, carried out by Collecte Localisation Satellite (CLS), an ensemble Kalman filter constrained by light-level position, sea surface temperature (SST, daily fields obtained at 9-km resolution by blending microwave and infrared SST from REMSS), and bottom topography (ETOPO2) was applied (Royer et al., 2005). Only deployment data lasting more than 1 month were analysed. Results Deployment duration and data retrieval Premature detachment of the tags was identified as a major problem in pop-up tagging of swordfish in the present study. Only one tag reported at its due date (60 d after deployment). Retention times were 13.83±17.32 and 56.96±61.79 d for stainless steel and nylon darts, respectively. Deployment duration ranged from 0 d (probably because of incorrect attachment of the dart) to 159 d. Data transmission was good in the area, with 1467±188 messages received per tag and an average rate of data corruption of 26.95%. No information was received from two of the tags deployed. Table 1 summarizes the data on deployment and reporting dates and positions. Table 1. Position and date of tag deployment and reporting for swordfish tagged in the SE Pacific. . . Deployment . Detachment . Tag . Hours per histogram . Latitude . Longitude . Date . Latitude . Longitude . Programmed . Actual . 73552 2 22°47′S 087°10′W 31 March 2007 2°27′S 097°41′W 60 60 73553 2 23°14′S 087°13′W 31 March 2007 24°25′S 086°08′W 60 8 73554 3 22°54′S 087°06′W 02 April 2007 22°40′S 088°40′W 90 8 73555 1 22°26′S 086°29′W 04 May 2007 16°18′S 089°56′W 30 20 73556 1 22°26′S 086°29′W 01 May 2007 20°38′S 088°05′W 30 9 73558 2 21°11′S 085°26′W 06 May 2007 20°58′S 086°08′W 60 8 73559 3 22°25′S 082°18′W 24 May 2007 – – 90 – 73561 1 22°21′S 086°52′W 30 March 2007 20°16′S 088°56′W 30 20 73563 4 23°01′S 087°31′W 28 April 2007 22°36′S 088°34′W 120 15 73564 6 22°10′S 083°52′W 30 May 2007 21°49′S 084°44′W 180 6 73565 6 22°03′S 084°27′W 30 May 2007 14°24′S 101°26′W 180 71 73566 6 19°12′S 083°21′W 17 June 2007 06°05′S 096°37′W 240 96 73568 12 19°05′S 083°35′W 23 June 2007 – – 300 – 73569 12 19°11′S 083°17′W 19 June 2007 19°00′S 083°36′W 360 3 73571 3 18°35′S 084°37′W 11 June 2007 14°43′S 091°19′W 180 166 73572 4 22°10′S 081°49′W 26 May 2007 09°31′S 099°12′W 120 49 73573 4 22°16′S 082°11′W 25 May 2007 21°30′S 083°21′W 120 6 73575 6 22°16′S 082°11′W 28 May 2007 19°32′S 085°03′W 180 11 73577 12 19°41′S 081°27′W 26 June 2007 19°30′S 082°25′W 300 7 73580 12 19°49′S 080°43′W 30 June 2007 07°39′S 105°25′W 360 104 73581 3 20°17′S 81°37′W 24 June 2007 20°14′S 082°07′W 180 5 . . Deployment . Detachment . Tag . Hours per histogram . Latitude . Longitude . Date . Latitude . Longitude . Programmed . Actual . 73552 2 22°47′S 087°10′W 31 March 2007 2°27′S 097°41′W 60 60 73553 2 23°14′S 087°13′W 31 March 2007 24°25′S 086°08′W 60 8 73554 3 22°54′S 087°06′W 02 April 2007 22°40′S 088°40′W 90 8 73555 1 22°26′S 086°29′W 04 May 2007 16°18′S 089°56′W 30 20 73556 1 22°26′S 086°29′W 01 May 2007 20°38′S 088°05′W 30 9 73558 2 21°11′S 085°26′W 06 May 2007 20°58′S 086°08′W 60 8 73559 3 22°25′S 082°18′W 24 May 2007 – – 90 – 73561 1 22°21′S 086°52′W 30 March 2007 20°16′S 088°56′W 30 20 73563 4 23°01′S 087°31′W 28 April 2007 22°36′S 088°34′W 120 15 73564 6 22°10′S 083°52′W 30 May 2007 21°49′S 084°44′W 180 6 73565 6 22°03′S 084°27′W 30 May 2007 14°24′S 101°26′W 180 71 73566 6 19°12′S 083°21′W 17 June 2007 06°05′S 096°37′W 240 96 73568 12 19°05′S 083°35′W 23 June 2007 – – 300 – 73569 12 19°11′S 083°17′W 19 June 2007 19°00′S 083°36′W 360 3 73571 3 18°35′S 084°37′W 11 June 2007 14°43′S 091°19′W 180 166 73572 4 22°10′S 081°49′W 26 May 2007 09°31′S 099°12′W 120 49 73573 4 22°16′S 082°11′W 25 May 2007 21°30′S 083°21′W 120 6 73575 6 22°16′S 082°11′W 28 May 2007 19°32′S 085°03′W 180 11 73577 12 19°41′S 081°27′W 26 June 2007 19°30′S 082°25′W 300 7 73580 12 19°49′S 080°43′W 30 June 2007 07°39′S 105°25′W 360 104 73581 3 20°17′S 81°37′W 24 June 2007 20°14′S 082°07′W 180 5 Open in new tab Table 1. Position and date of tag deployment and reporting for swordfish tagged in the SE Pacific. . . Deployment . Detachment . Tag . Hours per histogram . Latitude . Longitude . Date . Latitude . Longitude . Programmed . Actual . 73552 2 22°47′S 087°10′W 31 March 2007 2°27′S 097°41′W 60 60 73553 2 23°14′S 087°13′W 31 March 2007 24°25′S 086°08′W 60 8 73554 3 22°54′S 087°06′W 02 April 2007 22°40′S 088°40′W 90 8 73555 1 22°26′S 086°29′W 04 May 2007 16°18′S 089°56′W 30 20 73556 1 22°26′S 086°29′W 01 May 2007 20°38′S 088°05′W 30 9 73558 2 21°11′S 085°26′W 06 May 2007 20°58′S 086°08′W 60 8 73559 3 22°25′S 082°18′W 24 May 2007 – – 90 – 73561 1 22°21′S 086°52′W 30 March 2007 20°16′S 088°56′W 30 20 73563 4 23°01′S 087°31′W 28 April 2007 22°36′S 088°34′W 120 15 73564 6 22°10′S 083°52′W 30 May 2007 21°49′S 084°44′W 180 6 73565 6 22°03′S 084°27′W 30 May 2007 14°24′S 101°26′W 180 71 73566 6 19°12′S 083°21′W 17 June 2007 06°05′S 096°37′W 240 96 73568 12 19°05′S 083°35′W 23 June 2007 – – 300 – 73569 12 19°11′S 083°17′W 19 June 2007 19°00′S 083°36′W 360 3 73571 3 18°35′S 084°37′W 11 June 2007 14°43′S 091°19′W 180 166 73572 4 22°10′S 081°49′W 26 May 2007 09°31′S 099°12′W 120 49 73573 4 22°16′S 082°11′W 25 May 2007 21°30′S 083°21′W 120 6 73575 6 22°16′S 082°11′W 28 May 2007 19°32′S 085°03′W 180 11 73577 12 19°41′S 081°27′W 26 June 2007 19°30′S 082°25′W 300 7 73580 12 19°49′S 080°43′W 30 June 2007 07°39′S 105°25′W 360 104 73581 3 20°17′S 81°37′W 24 June 2007 20°14′S 082°07′W 180 5 . . Deployment . Detachment . Tag . Hours per histogram . Latitude . Longitude . Date . Latitude . Longitude . Programmed . Actual . 73552 2 22°47′S 087°10′W 31 March 2007 2°27′S 097°41′W 60 60 73553 2 23°14′S 087°13′W 31 March 2007 24°25′S 086°08′W 60 8 73554 3 22°54′S 087°06′W 02 April 2007 22°40′S 088°40′W 90 8 73555 1 22°26′S 086°29′W 04 May 2007 16°18′S 089°56′W 30 20 73556 1 22°26′S 086°29′W 01 May 2007 20°38′S 088°05′W 30 9 73558 2 21°11′S 085°26′W 06 May 2007 20°58′S 086°08′W 60 8 73559 3 22°25′S 082°18′W 24 May 2007 – – 90 – 73561 1 22°21′S 086°52′W 30 March 2007 20°16′S 088°56′W 30 20 73563 4 23°01′S 087°31′W 28 April 2007 22°36′S 088°34′W 120 15 73564 6 22°10′S 083°52′W 30 May 2007 21°49′S 084°44′W 180 6 73565 6 22°03′S 084°27′W 30 May 2007 14°24′S 101°26′W 180 71 73566 6 19°12′S 083°21′W 17 June 2007 06°05′S 096°37′W 240 96 73568 12 19°05′S 083°35′W 23 June 2007 – – 300 – 73569 12 19°11′S 083°17′W 19 June 2007 19°00′S 083°36′W 360 3 73571 3 18°35′S 084°37′W 11 June 2007 14°43′S 091°19′W 180 166 73572 4 22°10′S 081°49′W 26 May 2007 09°31′S 099°12′W 120 49 73573 4 22°16′S 082°11′W 25 May 2007 21°30′S 083°21′W 120 6 73575 6 22°16′S 082°11′W 28 May 2007 19°32′S 085°03′W 180 11 73577 12 19°41′S 081°27′W 26 June 2007 19°30′S 082°25′W 300 7 73580 12 19°49′S 080°43′W 30 June 2007 07°39′S 105°25′W 360 104 73581 3 20°17′S 81°37′W 24 June 2007 20°14′S 082°07′W 180 5 Open in new tab Depth and temperature Swordfish exhibited a typical diel vertical migration pattern, remaining close to the surface at night, and retreating deeper by day. Figure 1 illustrates the data on time spent at the predefined depth and temperature bins for the six tags analysed by day and night. Owing to the time-binning, these data include dawn and dusk events. By night, fish remained in the mixed layer around 100 m deep in the area where the fish were tagged, according to the depth–temperature profiles. Figure 2 shows the results of linear regression analyses between the average nocturnal depth and the visible moon fraction. For tag 73580, time-binning did not allow pure night-time data to be obtained. A significant positive correlation (ANOVA, p < 0.05) was observed for all fish tagged, varying from very weak (tag 73566) to moderately strong (tag 73565). Despite the noise associated with pop-up data (very summarized and with some data missing), the fish clearly remained deeper during full moon and closer to the surface during the new moon phase. Figure 1. Open in new tabDownload slide Histograms showing the depth and temperature frequency distributions of swordfish tagged in the Southeast Pacific by day and night. Figure 1. Open in new tabDownload slide Histograms showing the depth and temperature frequency distributions of swordfish tagged in the Southeast Pacific by day and night. Figure 2. Open in new tabDownload slide Linear regressions of average night-time depth and visible moon fraction (arcsine-transformed) for swordfish tagged in the Southeast Pacific. Figure 2. Open in new tabDownload slide Linear regressions of average night-time depth and visible moon fraction (arcsine-transformed) for swordfish tagged in the Southeast Pacific. By day, fish spent most of their time deeper than 400 m, usually reaching depths of >600 m. An analysis of depth–temperature profiles reveals that most fish engaged in occasional descents below 900 m, and the deepest dive recorded was 1136 m. This pattern is eventually modified. Frequently, a maximum appears at intermediate depths (150–250 m), and fish occasionally spend part of their time at the surface by day (so-called basking behaviour). Figure 3 shows the percentage of daylight hours in 50-m depth bins for fish 73552 plotted against dissolved oxygen concentration (ml l−1) over the course of its track. During the first few days after tagging, the fish stayed fairly shallow by day. Thereafter, however, a typical U-shaped movement pattern was recorded, with the fish staying close to the surface at night and in deeper water by day. These changes in depth coincided generally with dawn and dusk. During their vertical daily migration, swordfish are subjected to extreme changes in water temperature (maximum 21.4°C). By the end of April, however, this pattern is modified, the fish staying shallower by day, including surface basking. The change coincides with a decrease in the monthly average oxygen concentration in the water column. Environmental temperature ranged from 4 to 26.8°C and SST from 18.6 to 26.8°C. Figure 3. Open in new tabDownload slide Percentage of time at each 50-m depth bin during daytime of swordfish 73552 by date. The isolines represent dissolved oxygen concentration in ml l−1. Figure 3. Open in new tabDownload slide Percentage of time at each 50-m depth bin during daytime of swordfish 73552 by date. The isolines represent dissolved oxygen concentration in ml l−1. Horizontal movements Figure 4 shows the Kalman-filtered tracks of the six swordfish whose tags remained attached for more than 30 d. Initially, most tracked fish moved northwest after being tagged, regardless of the tagging date (end of March to end of June). Fish 73565 and 73580 initially travelled west for half a month and 1 month, respectively. This movement coincided with water cooling in the area where the fish were tagged. All swordfish remained in water with SST >18°C. Figure 4. Open in new tabDownload slide Individual SE Pacific swordfish tracks by month. Figure 4. Open in new tabDownload slide Individual SE Pacific swordfish tracks by month. The movement pattern was directed, i.e. the fish did not seem to stay in the same area for a long time, and the tracks estimated were fairly straight. The fish moved back south by late September/early October, when the SST of the water started to increase, but only two tags were still attached by then. Estimated daily displacements showed variability within and among individuals, without any obvious trend. Mean estimated daily displacement was 17.22±9.32 nautical miles d−1, individual values ranging between 12.01±6.38 and 28.78±11.21 nautical miles d−1. The northern and westernmost positions, 2°27′S and 101°59′W, coincide with the estimated pop-off positions of tags 73552 and 73580, respectively. Figure 5 shows the combined paths taken by the six fish analysed here. There was no association of fish with high-relief bottom structures. Figure 5. Open in new tabDownload slide Synthetic map of SE Pacific swordfish tracks by month. Figure 5. Open in new tabDownload slide Synthetic map of SE Pacific swordfish tracks by month. Discussion Premature detachment was the main problem with swordfish pop-up tagging in this study. In eight cases, premature detachment seemed to be attributable to fish death, detected as a descent at a constant speed down to 1800 m, when the RD1800 device would sever the tether. This is probably accounted for by the long set duration, which could last more than 8 h, and is the main disadvantage of opportunistic tagging aboard commercial vessels. Recent research (Neilson et al., 2009) has proved the feasibility of pop-up tagging of swordfish without high mortality. Although the observers were trained to select and tag only those fish showing no signs of harm, not bleeding, and active, states confirmed by the analysis of video recordings, these criteria do not necessarily reflect fish condition. However, adverse effects resulting from tagging cannot be ruled out definitively. Premature detachment is a common problem of pop-up tags (e.g. Holdsworth et al., 2007; Loefer et al., 2007), regardless of the species studied, and it can be attributed to various causes aside from fish death. Continuous rubbing of the tether monofilament against the dart, swivel, crimps, or guillotine may cause it to break. Premature corrosion or breakage of the tag's metal pin also cannot be ruled out. In the Mediterranean Sea, several pop-up-tagged bluefin tuna (Thunnus thynnus) whose tags detached prematurely have been recaptured carrying the whole tether intact (FJA, pers. obs.; G. De Metrio, pers. comm.). However, a recent study on swordfish pop-up tagging (Neilson et al., 2009) has achieved long retention times, up to 411 d, one of the longest periods of attachment of pop-up satellite tags reported for any fish species. In general, satellite transmission was good in the study area, with ca. 1500 messages received per tag and a low corruption rate. Two tags did not transmit information. Hays et al. (2007) identified the failure of the saltwater switch as the main cause of signal cessation, especially in long-term deployments. However, battery failure, seawater inundation, or hardware damage cannot be rejected as causes of premature cessation of the signal. In some cases, unusual vertical behaviour consisting of stays at the surface for many hours, followed by deep dives, was observed before premature tag release. The cause is unknown, but it could be related to fish predation or scavenging, as has been described for white marlin (Tetrapturus albidus) and opah (Lampris guttatus; Kerstetter et al., 2004). Swordfish undertake diel vertical migration, as do other large pelagic species such as bluefin tuna (Teo et al., 2007), bigeye tuna (Thunnus obesus; Schaefer and Fuller, 2002; Musyl et al., 2003), and yellowfin tuna (Thunnus albacares; Schaefer et al., 2007). In swordfish, such behaviour was described by Carey and Robinson (1981) using acoustic telemetry. The behaviour seems to mimic the movement of mesopelagic organisms in the deep scattering layer, where swordfish feed (Carey, 1990). At night, swordfish always stayed in the mixed layer, where they can feed and, at the same time, recover from thermal or oxygen debt acquired by day. The variation in average depth at night with the moon phase was suggested by Carey and Robinson (1981), although those authors only worked with discrete data from different fish. Recently, Loefer et al. (2007) presented evidence of this relationship using pop-up tags in the Northwest Atlantic. From our data (e.g. Figure 2), it seems that the maximum depth by night was usually reached close to the full moon. This average depth, in the data we analysed, was always above the thermocline. Although more data are required to formulate definitive conclusions, the depth of the thermocline appears to limit the vertical distribution of swordfish by night. By day, swordfish typically descend to deep layers just before dawn, and bottom out, usually >500 m, shortly after sunrise. They remain there until dusk, when they return to the mixed layer. Although time-binning of the pop-up tags used in the present study does not allow accurate estimation of the time at which these movements take place, it seems from the analysis of the time at each depth bin that they occur within 2 h, around sunrise and sunset. The maximum depth recorded in this study was >1100 m, but dives below 900 m were observed in five of the six tags analysed. During these vertical movements, swordfish are subject to wide temperature variability (up to 21.4°C in this study), sometimes in <1 h, indicating a remarkable adaptive capacity to utilize habitats with low oxygen and temperature. Swordfish have an ability to occupy such deep water as a consequence of several different physiological adaptations, namely the presence of (i) a thermogenic organ in the head, the brain heater (Carey, 1990); (ii) large eyes, which allow them to pursue their prey in dim light; and (iii) the large mass of white muscle, which might make swordfish more resistant to anoxia than other large pelagic species and allow them to accumulate oxygen debt while foraging at great depth (Carey and Robinson, 1981). Some modifications of this U-shaped pattern were observed. During the first few days after tagging, four of the six swordfish stayed fairly shallow, possibly related to the stress caused by being caught and tagged. A possible explanation for this change in behaviour is that, although well adapted to deep environments, swordfish probably have a fast rate of recovery in water with high oxygen concentration and warm temperature, which are usually found shallower. However, more information on the physiology of the species is needed to make this a definitive conclusion. After the “recovery” period and during most days, the tagged swordfish demonstrated the typical U-shaped diving behaviour. Occasionally, a second time-frequency maximum was found around 150–250 m, perhaps related to the presence there of prey, or the need to increase body temperature. Some time after tagging, as fish moved northwest, the U-shaped pattern tended to be modified. On some days, fish combined deep dives over time at the surface by day (basking behaviour), whereas on other days, they seemed to forage shallower by day. There was no relationship between SST or water-column stratification and fish behaviour. This was observed at both high (>26°C) and low (<20°C) SST. Carey and Robinson (1981) suggested that basking behaviour, as well as the shallow depth maxima, of swordfish off Baja California could be related to the presence of an oxygen-minimum layer. In the eastern Pacific, there is a well-developed oxygen-minimum zone, typical of oceanic regions with high primary productivity. Moreover, there is a clear variation in the intensity, vertical position, and thickness of the oxygen-minimum zone related to latitude there (Helly and Levin, 2004; Stramma et al., 2008). Shallow behaviour by day was observed for fish 73552 (Figure 3), fish 73566, and the end of the tracking period of fish 73572 in areas with low concentrations of oxygen (<0.5 ml l−1) at intermediate depths (ca. 200–600 m). Fish 73565 and 73580 did not seem to enter areas with oxygen concentration <1 ml l−1, and the U-shaped pattern was maintained during most of the time they were tracked. However, fish 73571, which also seemed to enter areas of very low oxygen concentration, maintained its typical U-shaped pattern during most of its tracking period. It must be noted, however, that there are uncertainties associated with the estimates of dissolved oxygen concentration used in the present study: errors in geolocation estimates, values from the World Ocean Atlas consisting of climatological monthly means at discrete depths, and time-at-depth-binning limited. In the area where Carey and Robinson (1981) carried out their study, the oxygen minimum extended deeper (ca. 800 m), which could explain why all the swordfish they tagged spent most of their time shallower than 100 m. Other research (Prince and Goodyear, 2006) has shown how cold hypoxic water restricts the depth distribution of billfish in the eastern tropical Pacific. However, the possibility that changes in vertical behaviour respond to the distribution of the prey cannot be ruled out. Despite the ability of swordfish to tolerate a wide range of temperature, their distribution seems to be highly affected by SST. In the current study, the minimum SST recorded was 18.6°C. Estimated fish LJFL ranged from 150 to 180 cm in the present study, corresponding to weights of ca. 40–80 kg, according to Uchiyama et al. (1999). Palko et al. (1981) reported that fish <90 kg are seldom seen in water <18°C in the Northwest Atlantic. As water temperature decreased, the fish moved northwest. By the onset of spring, from September to early October, the two fish still with tags travelled back south. This movement could also be related to food availability because upwelling off Peru is year-round, but off Chile only during the austral spring and summer. De Sylva (1962, cited in Hinton et al., 2005) reported an apparent northward migration of swordfish off northern Chile in April and May. Similarly, Takahashi et al. (2003) hypothesized a cyclic migration of swordfish in the Northwest Pacific between food-rich, cold-current areas during summer and the subtropical wintering area. Neilson et al. (2009) recently described, using PSAT tags, a consistent migration pattern in the Northwest Atlantic. Fish tagged off Canada travelled to tropical waters by autumn and moved back to the same foraging grounds in temperate waters by early spring. Previous studies have reported an association between swordfish distribution and thermal fronts (Podestá et al., 1993; Sedberry and Loefer, 2001). In our case, no such relationship was observed, but this could be due partially to geolocation errors, mainly latitude (Sibert et al., 2009). For swordfish, their vertical behaviour makes it difficult to obtain good estimates of position. Light-level geolocation is based on determining dawn and dusk accurately. As mentioned above, the greatest variations in depth take place precisely at dawn and dusk, making it difficult to obtain good light curves from which to determine position. Swordfish apparently associate with bottom topographic structures (Carey and Robinson, 1981; Carey, 1990; Podestá et al., 1993; Sedberry and Loefer, 2001), but in our study, there were few remarkable high-relief structures between the area where the fish were tagged (Nazca Ridge) and the pop-off position, regardless of geolocation error. Although production models indicate that catch per unit effort (cpue) of swordfish in the Southeast Pacific is greater than that corresponding to average MSY (Hinton et al., 2005), there is some concern about the sustainability of the current levels of exploitation because of uncertainties associated with these evaluations. Fishery-based cpue data, one of the main inputs to stock assessments, do not necessarily reflect real abundance, especially of very mobile species (Brill and Lutcavage, 2001). Fish availability to a certain gear type may vary depending on SST, water column structure, and time of day. Ideally, information on the migration patterns and habitat preferences of swordfish should be taken into account in future stock assessments, in order to consider changes in the vulnerability of fish to different gear types, mixing between putative stocks, and other factors. Moreover, the extent of migratory movement can serve to estimate the probability of local depletion in certain areas. As an example, Bigelow et al. (2002) found significant differences between the nominal and standardized cpue series of bigeye tuna in the western and central Pacific when incorporating habitat preferences into their model. Similarly, the incorporation of habitat information could serve, in some cases, to explain the discrepancies observed in cpue trends of swordfish between night-set surface longlines targeting swordfish and day-set deep longline fisheries mostly targeting tuna (Anon., 2007). A consensus has not been reached on the population structure of swordfish in the Pacific (Reeb et al., 2000; Alvarado Bremer et al., 2006; Hinton and Alvarado Bremer, 2007; Kasapidis et al., 2008). The present study is, as far as we can ascertain, the first attempt to describe migratory patterns and habitat preferences of swordfish in the Southeast Pacific through pop-up satellite tagging. Our results support the current assumption of an independent stock in the Southeast Pacific. However, the northernmost latitude reached by the fish we tagged was 2°27′S (pop-off position of fish 73552), while it was still heading north, whereas the northern boundary of the southern stock is currently taken to be 5°S. Moreover, no spawning area has, so far, been described for this putative stock. The present study covers just a small spatio-temporal region, and experience from conventional tagging studies (Neilson et al., 2007) reveals that migration patterns are influenced by the area/time coverage of the tagging. The migration patterns deduced would, therefore, change if the area/time coverage of tagging was broader. In recent years, electronic tag data have provided evidence of greater spatial distributions than previously assumed for several tuna and billfish species (e.g. Atlantic bluefin tuna, Pacific bigeye tuna). Incorporation of this information into fisheries management, as it becomes available, will improve the effectiveness of management measures and hopefully reduce the uncertainties in stock assessments. Although more research is needed, with more fish being tagged and other seasons and areas covered, PSAT tagging, along with other information, such as fishery data, genetics, or biochemical markers, will certainly provide insight into the population structure of Pacific swordfish, which is crucial to the effective assessment of stocks. Acknowledgements We thank B. García, O. Soto, and D. Espino for their manifold efforts, the crew of FV “Makus” and “Mariané” for their collaboration in the tagging operations, and IAD for providing the logistics. M. E. Lutcavage, K. M. Schaefer, D. W. Fuller, G. De Metrio, M. Deflorio, B. A. Block, J. D. Neilson, and P. Vélez provided support at different stages of the study, and E. D. Prince kindly donated the nylon darts and offered helpful suggestions. Collecte Localisation Satellite are acknowledged for their excellent post-processing of geolocation data, and we also thank two referees for useful suggestions that helped to improve the manuscript considerably. The study was funded by the IEO project SWOATL0710. References Alvarado Bremer J. R. , Hinton M. G. , Greig T. W. . Evidence of spatial heterogeneity in Pacific swordfish (Xiphias gladius L.) revealed by the analysis of ldh-A sequences , Bulletin of Marine Science , 2006 , vol. 79 (pg. 493 - 503 ) Google Scholar OpenURL Placeholder Text WorldCat Anon. Report of the 2006 Atlantic Swordfish Stock Assessment Session , Collective Volume of Scientific Papers ICCAT , 2007 , vol. 60 (pg. 1787 - 1896 ) OpenURL Placeholder Text WorldCat Bigelow K. A. , Hampton J. , Miyabe N. . Application of a habitat-based model to estimate effective longline fishing effort and relative abundance of Pacific bigeye tuna (Thunnus obesus) , Fisheries Oceanography , 2002 , vol. 11 (pg. 143 - 155 ) Google Scholar Crossref Search ADS WorldCat Brill R. W. , Lutcavage M. E. . Understanding environmental influences on movements and depth distributions of tunas and billfishes can significantly improve population assessments , American Fisheries Society Symposium , 2001 , vol. 25 (pg. 179 - 198 ) Google Scholar OpenURL Placeholder Text WorldCat Carey F. G. . Stroud R. H. . Further acoustic telemetry observations of swordfish , Planning the Future of Billfishes—Research and Management in the 90s and Beyond. 2. Contributed Papers. Proceedings of the Second International Billfish Symposium, Kailua-Kona, HI, 1–5 August 1988 , 1990 Savannah, GA National Coalition for Marine Conservation, Inc. (pg. 103 - 122 ) Marine Recreational Fisheries, 13. 321 pp. Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Carey F. G. , Robinson B. H. . Daily patterns in the activities of swordfish, Xiphias gladius, observed by acoustic telemetry , Fishery Bulletin US , 1981 , vol. 79 (pg. 277 - 292 ) Google Scholar OpenURL Placeholder Text WorldCat Dewar H. , Polovina J. . Deploying satellite tags on swordfish using the California harpoon fleet , Pelagic Fisheries Research Program Newsletter , 2005 , vol. 10 (pg. 4 - 6 ) Google Scholar OpenURL Placeholder Text WorldCat García H. E. , Locarnini R. A. , Boyer T. P. , Antonov J. I. . Levitus S. . World Ocean Atlas 2005. 3. Dissolved Oxygen, Apparent Oxygen Utilization, and Oxygen Saturation , 2006 Washington, DC NOAA Atlas NESDIS 63, U.S. Government Printing Office pg. 342 Google Scholar Hays G. C. , Bradshaw C. J. A. , James M. C. , Lovell P. , Sims D. W. . Why do Argos satellite tags deployed on marine animals stop transmitting? , Journal of Experimental Marine Biology and Ecology , 2007 , vol. 349 (pg. 52 - 60 ) Google Scholar Crossref Search ADS WorldCat Helly J. J. , Levin L. A. . Global distribution of naturally occurring marine hypoxia on continental margins , Deep Sea Research I , 2004 , vol. 51 (pg. 1159 - 1168 ) Google Scholar Crossref Search ADS WorldCat Hinton M. G. , Alvarado Bremer J. . Stock structure of swordfish in the Pacific Ocean , 2007 IATTC Working Group to Review Stock Assessments, 8th Meeting, La Jolla, CA, 7–11 May 2007. Document SAR-8-11 Google Scholar Hinton M. G. , Bayliff W. H. , Suter J. M. . Assessment of swordfish in the eastern Pacific Ocean , Inter-American Tropical Tuna Commission, Stock Assessment Report , 2005 , vol. 5 (pg. 291 - 336 ) Google Scholar OpenURL Placeholder Text WorldCat Holdsworth J. C. , Sippel T. J. , Paul P. J. . An investigation into swordfish stock structure using satellite tag and release methods , 2007 Honolulu, HI Biology Specialist Working Group Paper WCPFC-SC3-2007/BI WP-3. 3rd Regular Session of the Scientific Committee of the Western and Central Pacific Fisheries Commission, 13–24 August 2007 Google Scholar Kasapidis P. , Magoulas A. , García-Cortés B. , Mejuto J. . Stock structure of swordfish (Xiphias gladius) in the Pacific Ocean using microsatellite DNA markers. Biology Specialist Working Group Paper WCPFC-SC4-2008/BI WP-4 , 2008 Port Moresby, Papua New Guinea 4th Regular Session of the Western and Central Pacific Fisheries Commission, 11–22 August 2008 Google Scholar Kerstetter D. W. , Polovina J. J. , Graves J. E. . Evidence of shark predation and scavenging on fishes equipped with pop-up satellite archival tags , Fishery Bulletin US , 2004 , vol. 102 (pg. 750 - 756 ) Google Scholar OpenURL Placeholder Text WorldCat Kolody D. , Davies N. , Campbell R. . South-west Pacific swordfish stock status summary from multiple approaches. Stock Assessment Specialist Working Group paper WCPFC-SC2-2006/SA WP-7 , 2006 2nd Regular Session of the Scientific Committee of the Western and Central Pacific Fisheries Commission, Manila, Philippines, 7–18 August 2006 Google Scholar Loefer J. K. , Sedberry G. R. , McGovern J. C. . Nocturnal depth distribution of western North Atlantic swordfish (Xiphias gladius, Linnaeus, 1758) in relation to lunar illumination , Gulf and Caribbean Research , 2007 , vol. 19 (pg. 83 - 88 ) Google Scholar Crossref Search ADS WorldCat Musyl M. K. , Brill R. W. , Boggs C. H. , Curran D. S. , Kazama T. K. , Seki M. P. . Vertical movements of bigeye tuna (Thunnus obesus) associated with islands, buoys, and seamounts near the main Hawaiian Islands from archival tagging data , Fisheries Oceanography , 2003 , vol. 12 (pg. 152 - 169 ) Google Scholar Crossref Search ADS WorldCat Neilson J. D. , Paul S. D. , Smith S. C. . Stock structure of swordfish (Xiphias gladius) in the Atlantic: a review of the non-genetic evidence , Collective Volume of Scientific Papers ICCAT , 2007 , vol. 61 (pg. 25 - 60 ) Google Scholar OpenURL Placeholder Text WorldCat Neilson J. D. , Smith S. , Royer F. , Paul S. D. , Porter J. M. , Lutcavage M. . Nielsen J. L. , Arrizabalaga H. , Fragoso N. , Hobday A. , Lutcavage M. , Sibert J. . Investigations of horizontal movements of Atlantic swordfish using pop-up satellite archival tags , Tagging and Tracking of Marine Animals with Electronic Devices. Series: Reviews: Methods and Technologies in Fish Biology and Fisheries, 9 , 2009 New York Springer (pg. 145 - 159 ) 452 pp Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Palko B. J. , Beardsley G. L. , Richards W. J. . Synopsis of the biology of the swordfish, Xiphias gladius Linnaeus , 1981 FAO Fisheries Synopsis, 127 Google Scholar Podestá G. , Browder J. A. , Hoey J. J. . Exploring the association between swordfish catch rates and thermal fronts on US longline grounds in the western North Atlantic , Continental Shelf Research , 1993 , vol. 13 (pg. 253 - 277 ) Google Scholar Crossref Search ADS WorldCat Prince E. D. , Goodyear C. P. . Hypoxia-based habitat compression of tropical pelagic fishes , Fisheries Oceanography , 2006 , vol. 15 (pg. 451 - 464 ) Google Scholar Crossref Search ADS WorldCat Reeb C. A. , Arcangeli L. , Block B. A. . Structure and migration corridors in Pacific populations of the swordfish, Xiphias gladius, as inferred through analyses of mitochondrial DNA , Marine Biology , 2000 , vol. 136 (pg. 1123 - 1131 ) Google Scholar Crossref Search ADS WorldCat Royer F. , Fromentin J-M. , Gaspar P. . A state-space model to derive bluefin tuna movement and habitat from archival tags , Oikos , 2005 , vol. 109 (pg. 473 - 484 ) Google Scholar Crossref Search ADS WorldCat Schaefer K. M. , Fuller D. W. . Movements, behavior, and habitat selection of bigeye tuna (Thunnus obesus) in the eastern equatorial Pacific, ascertained through archival tags , Fishery Bulletin US , 2002 , vol. 100 (pg. 765 - 788 ) Google Scholar OpenURL Placeholder Text WorldCat Schaefer K. M. , Fuller D. W. , Block B. A. . Movements, behavior, and habitat utilization of yellowfin tuna (Thunnus albacares) in the northeastern Pacific Ocean, ascertained through archival tag data , Marine Biology , 2007 , vol. 152 (pg. 503 - 525 ) Google Scholar Crossref Search ADS WorldCat Sedberry G. R. , Loefer J. K. . Satellite telemetry tracking of swordfish, Xiphias gladius, off the eastern United States , Marine Biology , 2001 , vol. 139 (pg. 355 - 360 ) Google Scholar Crossref Search ADS WorldCat Sibert J. R. , Nielsen A. , Musyl M. K. , Leroy B. , Evans K. . Nielsen J. L. , Arrizabalaga H. , Fragoso N. , Hobday A. , Lutcavage M. , Sibert J. . Removing bias in latitude estimated from solar irradiance series , Tagging and Tracking of Marine Animals with Electronic Devices. Series: Reviews , 2009 New York Methods and Technologies in Fish Biology and Fisheries, 9. Springer (pg. 311 - 322 ) 452 pp Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Stramma L. , Johnson G. C. , Sprintall J. , Mohrholz V. . Expanding oxygen-minimum zones in the tropical oceans , Science , 2008 , vol. 320 (pg. 655 - 658 ) Google Scholar Crossref Search ADS PubMed WorldCat Takahashi M. , Okamura H. , Yokawa K. , Okazaki M. . Swimming behaviour and migration of a swordfish recorded by an archival tag , Marine and Freshwater Research , 2003 , vol. 54 (pg. 527 - 534 ) Google Scholar Crossref Search ADS WorldCat Teo S. L. H. , Boustany A. , Dewar H. , Stokesbury M. J. W. , Weng K. C. , Beemer S. , Seitz A. C. , et al. Annual migrations, diving behavior, and thermal biology of Atlantic bluefin tuna, Thunnus thynnus, on their Gulf of Mexico breeding grounds , Marine Biology , 2007 , vol. 151 (pg. 1 - 18 ) Google Scholar Crossref Search ADS WorldCat Uchiyama J. H. , DeMartini E. E. , Williams H. A. . Length–weight interrelationships for swordfish, Xiphias gladius L., caught in the central North Pacific , 1999 NOAA Technical Memorandum, NMFS-SWFSC-284 pg. 82 Google Scholar Zar J. H. . Biostatistical Analysis , 1996 Upper Saddle River, NJ, USA Prentice-Hall pg. 662 Google Scholar © 2009 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved. For Permissions, please email: [email protected] © 2009 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved. For Permissions, please email: [email protected]

Vilata, Juan; Oliva, Doris; Seplveda, Maritza

doi: 10.1093/icesjms/fsp250pmid: N/A

Vilata, J., Oliva, D., and Seplveda, M. 2010. The predation of farmed salmon by South American sea lions (Otaria flavescens) in southern Chile. ICES Journal of Marine Science, 67: 475482.The South American sea lion Otaria flavescens is abundant off southern Chile. Because Chilean salmon farming has experienced an explosive growth in the past two decades, interactions between O. flavescens and this industry have increased. Fieldwork, including in situ behavioural observations, was carried out at three salmon farms off southern Chile from May to July 2008. The aim was to analyse possible patterns in the interactions and to evaluate whether they were influenced by the endogenous circa-rhythms of the species, prey size, tidal flux, and the use of an acoustic harassment device (AHD). The results showed that the attacks by O. flavescens followed seasonal patterns, with salmon predated more in autumn and winter, and daily patterns, with more interactions at night. In addition, attacks were more frequent on larger salmon, suggesting the existence of a prey-size preference. More sea lions were sighted at the ebb and flow tide peaks, when currents are stronger, suggesting that currents linked to tidal flux might facilitate the access of the sea lions to the farmed salmon. Although the use of AHDs appeared positive at one site, there is a strong suspicion that their efficacy may be site-specific.

Dolgov, Andrey V.; Johannesen, Edda; Heino, Mikko; Olsen, Erik

doi: 10.1093/icesjms/fsp254pmid: N/A

Dolgov, A. V., Johannesen, E., Heino, M., and Olsen, E. 2010. Trophic ecology of blue whiting in the Barents Sea. ICES Journal of Marine Science, 67: 483493.Blue whiting (Micromesistius poutassou) are distributed throughout the North Atlantic, including the Norwegian and Barents Seas. In recent years, both abundance and distribution of blue whiting in the Barents Sea have increased dramatically. Therefore, to evaluate the trophic impact of this increase, we analysed the diet of the species. In all, 54 prey species or taxa were identified, the main prey being krill. However, the diet varied geographically and ontogenetically: the proportion of fish in the diet was higher in large blue whiting and in the north of the range. Blue whiting overlap geographically with other pelagic species at the edge of their distribution in the Barents Sea, with juvenile herring in the south, with polar cod in the north, and with capelin in the northeast. The overlap in diet between blue whiting and these other pelagic species ranged from 6 to 86 and was greatest with capelin in areas where both species feed on hyperiids and krill. The importance of blue whiting as prey for predatory fish was highest in the areas of greatest abundance, but overall, blue whiting were seemingly unimportant as prey of piscivorous fish in the Barents Sea.

Large, Philip A.; Diez, Guzman; Drewery, James; Laurans, Martial; Pilling, Graham M.; Reid, David G.; Reinert, Jkup; South, Andrew B.; Vinnichenko, Vladimir I.

doi: 10.1093/icesjms/fsp264pmid: N/A

Large, P. A., Diez, G., Drewery, J., Laurans, M., Pilling, G. M., Reid, D. G., Reinert, J., South, A. B., and Vinnichenko, V. I. 2010. Spatial and temporal distribution of spawning aggregations of blue ling (Molva dypterygia) west and northwest of the British Isles. ICES Journal of Marine Science, 67: 494501.Fisheries on blue ling in ICES Areas Vb, VI, VII, and XIIb have mostly targeted spawning aggregations. ICES has repeatedly advised that blue ling are susceptible to sequential depletion of spawning aggregations and that closed areas to protect spawning aggregations should be maintained and expanded where appropriate. Information from a range of sources, including fishers, is analysed, and five main spawning areas are identified: (i) along the continental slope northwest of Scotland (ICES Division VIa); (ii) on, around, and northwest of Rosemary Bank (VIa); (iii) on the southern and southwestern margins of Lousy Bank (Vb); (iv) on the northeastern margins of Hatton Bank (VIb); and (v) along the eastern and southern margins of Hatton Bank (VIb). From the information available, it is suggested that, for management purposes, peak spawning be considered to take place at depths of 7301100 m between March and May inclusive in VIa and Vb, and during March and April in VIb. Based largely on this information, the European Commission (EC) introduced in 2009 protection areas for spawning aggregations of southern blue ling in European Union (EU) waters within ICES Division VIa.