A framework for risk analysis in fisheries decision-makingLane, D. E.; Stephenson, R. L.
doi: 10.1006/jmsc.1997.0237pmid: N/A
Failures in fisheries management have been linked to our inability to embrace the inherent uncertainty of fisheries systems. Fisheries decisions should be made on the basis of integrated evaluations of strategy alternatives, where comparisons of comprehensive scenarios incorporate strategic biological and socio-economic objectives and constraints, and explicitly take account of system uncertainties and evaluated risk. This paper investigates the requirements for integrated decision-making for fisheries systems. It is argued that conceptual change is required, and that such change will form the basis for interdisciplinary studies in “fisheries management science”. Founded on the principles of decision analysis developed within the field of operational research/management science, the fisheries management science approach provides the requisite methodologies for risk analysis and its components of risk assessment and risk management, and for improved decision support. An illustrative case study based on the herring fishery in NAFO divisions 4WX is used to demonstrate the proposed methodology.
Distribution and abundance of the fished population of Loligo forbesi in Scottish waters: analysis of research cruise dataPierce, G. J.; Bailey, N.; Stratoudakis, Y.; Newton, A.
doi: 10.1006/jmsc.1997.0257pmid: N/A
Length-frequency data on squid (Loligo forbesi) collected during trawling surveys in Scottish waters from 1980 to 1994 were analysed to describe temporal and spatial patterns in abundance and to examine the prospects for using survey abundance to forecast fishery abundance. Loligo was patchily distributed in space and time. Distribution patterns in the North Sea in February appeared to be strongly related to bottom temperature (squid avoided waters <7°C) and, to a lesser extent, salinity (more squid in more saline water). For other areas and times, no temperature or salinity data were available, but there were trends for squid on the west coast to be more abundant in westerly areas and higher latitudes, and for squid at Rockall to be more abundant in shallow water. Inter-annual trends in abundance differed between the North Sea, west coast and Rockall, but average survey abundances for the North Sea and west coast tended to be positively correlated. For the North Sea and west coast, survey abundance was positively correlated with fishery abundance for the same month and area, and average abundance for the February North Sea survey was a reasonable predictor of commercial CPUE in the autumn of the same year (the peak of the fishery). Some of the observed trends were consistent with the existence of a stock-recruitment relationship but may indicate that abundance in a given calendar year is linked to climatic factors.
Tributyltin inputs to the North Sea from shipping activities, and potential risk of biological effectsDavies, Ian M.; Bailey, Susan K.; Harding, Melanie J.C.
doi: 10.1006/jmsc.1997.0275pmid: N/A
The mechanisms leading to an annual input of tributyltin (TBT) to the North Sea from shipping are discussed. It is estimated that the gross annual input of TBT to the North Sea was 68 tonnes.A simple numerical model of the North Sea has been applied to the input data, and indicates that the greatest risk of biological effects of TBT from commercial vessels would be expected in areas of the south-eastern North Sea (NSTF Areas 4, 5), and off eastern England (Area 3ii). Low intensity of impact was indicated in the northern (Areas 1, 2, 3i) and north-central (Area 7i) North Sea. The sensitivity of the model output to variations in critical parameters of the behaviour and inputs of TBT are discussed, and are found to have minor effects on the overall conclusions.The estimates of relative risk of biological effects from TBT broadly reflect the impacts observed in dogwhelks (Nucella lapillus L.) in North Sea coastal areas.
Annual production of fish larvae and their prey in relation to size-fractionated primary production (Scotian Shelf, NW Atlantic)*Mousseau, Laure; Fortier, Louis; Legendre, Louis
doi: 10.1006/jmsc.1997.0224pmid: N/A
The annual cycles of abundance of fish larvae and their zooplankton prey were analysed in relation to the biomass and production of size-fractionated phytoplankton on the Scotian Shelf (North-west Atlantic). Outside the spring bloom of large (>5 μm) phytoplankton (February to April), the small-sized fraction of phytoplankton (<5 μm) contributed the bulk of total primary production. The production of copepod nauplii and copepodites was sustained throughout the year and fish larvae specializing on copepod prey occurred year-round. Species feeding on a mixed diet of copepods, cladocerans and/or appendicularians were restricted to periods of maximum temperature in summer and early autumn. Two short trophic pathways (two links) from primary producers to fish larvae were identified: the herbivorous food chain (large phytoplankton→calanoid copepods→fish larvae) and the large-microphage shunt of the microbial food web (small phytoplankton→appendicularians/pteropods→fish larvae). The year-round production of fish larvae and the fact that several of their major prey (appendicularians, thecosome pteropods, cladocerans, and cyclopoid copepods) exploit the microbial food web, challenge the tenet that the feeding of marine fish larvae depends primarily on the reproduction of herbivorous calanoid copepods grazing the spring and autumn blooms of large phytoplankton.
Tracking herring schools with a high resolution sonar. Variations in horizontal area and relative echo intensityMisund, Ole Arve; Fernö, Anders; Pitcher, Tony; Totland, Bjørn
doi: 10.1006/jmsc.1997.0228pmid: N/A
Fourteen herring schools off northern Norway were tracked for about 1 hour each by the 95 kHz Simrad SA950 sonar onboard R/V “G.O. Sars” in May 1994. The sonar was connected to a work station that contained software for reading the echo telegrams of the sonar, printing of an echogram, automatic detection and measurement of schools, and logging of the sonar data. The horizontal area and relative echo intensity of the schools were recorded ping by ping as well as swimming depth and distance and bearing to the vessel. The position, speed and heading of the vessel were also recorded. Inter- and intra-school events as interpreted from the sonar display were recorded in a separate protocol during the school tracking. The recorded horizontal area and relative echo intensity of the schools varied considerably. Linear models with school area or relative echo intensity as dependent variables, and with range, tilt, speed and swimming angle relative to the sonar beam as continuous effects, did not explain more than 15% and 30% of the observed variations for most schools, respectively. There was a negative correlation between relative echo intensity and range for all schools. Inter- and intra-school events occurred at average rates of about 14 minutes, and inter-school events such as split and joint influenced school size. The sound absorption and the degree to which the sonar beam insonifies the schools in the vertical plane are proposed as the major sources of variation for recorded horizontal area and relative echo intensity of the schools.
Ambient temperature and distribution of north-east Arctic codOttersen, Geir; Michalsen, Kathrine; Nakken, Odd
doi: 10.1006/jmsc.1997.0232pmid: N/A
Many studies on the effects of temperature on fish distribution and population parameters have considered the temperature and its variability at fixed stations or sections rather than the ambient temperature actually surrounding the fish. In the present paper ambient winter temperature was estimated for 1–7 year-old north-east Arctic cod in the period 1988–1995 from spatial distributions of fish density and temperature. Four different estimates were calculated for each age and year based on fish density observations from acoustic and bottom-trawl surveys and temperature recordings at the bottom, as well as averaged from 100 m depth to bottom. The estimates of ambient temperature were compared with each other and with temperature series in fixed areas and a standard section, the Kola meridian. The inter-annual variability in ambient winter temperature was found to be larger than in the Kola section series. Older fish were found at higher temperatures. For the younger age groups the range extended eastwards when numbers were high. This could explain the observed decrease of mean ambient temperatures in which cod were found during a relatively warm period in the Barents Sea. The mean ambient temperatures are also compared with the temperatures used for calculations of consumption rate by cod in the ICES Working groups.
Assessment of the spatial structure and biomass evaluation of Nephrops norvegicus (L.) populations in the northwestern Mediterranean by geostatisticsMaynou, Francesc X.; Sardà, Francisco; Conan, Gérard Y.
doi: 10.1006/jmsc.1997.0236pmid: N/A
The spatial distribution and biomass of Nephrops norvegicus were assessed by trawling over commercial fishing grounds (“Serola”, off Barcelona, Spain) during two surveys (spring and fall 1991), using geostatistical methods. The surveys were set 6 months apart, in order to analyse possible seasonal differences. In the present surveys, Norway lobster was caught between 200 and 600 m depth, with peak abundance at about 400 m. The analysis of the structure of spatial correlation by means of semivariograms showed that densities of Nephrops norvegicus were spatially autocorrelated and lobster populations were distributed in high-density patches 6 to 9 km in diameter. No spatial segregation per biological category (size or sex) was detected. The semivariograms were consistent for all biological categories. A strong linear relationship between local mean and standard deviation (proportional effect) was modelled by the relative semivariogram. Relative experimental semivariograms were fitted to a spherical model. The shape of the semivariogram, and the spatial autocorrelation structure of Norway lobster populations, remained stable over the two surveys. The density of Nephrops norvegicus available to the experimental gear was mapped by point kriging. High-density patches of different biological categories exactly conformed and remained stable over the two surveys, showing a certain intra-annual stability. However, mean densities and overall abundance (computed by global kriging) decreased sharply in the fall survey. This was accounted for by means of knowledge on the biology of the species for the same area. The biological characteristics of Nephropspopulations in the area studied are similar to those of other Mediterranean and Atlantic populations, hence our results are not restricted to the study area. We conclude that the geostatistical analysis approach, which takes into consideration the spatial auto-correlation structure of the populations, is adequate for the direct biomass estimation and assessment of Nephrops harvestable stock.
Seasonal variation in the importance of pelagic fish in the diet of piscivorous fish in the Moray Firth, NE Scotland: a response to variation in prey abundance?Greenstreet, Simon P.R.; McMillan, Julie A.; Armstrong, Eric
doi: 10.1006/jmsc.1997.0258pmid: N/A
Species-ranked frequency distributions (k-dominance curves) indicated that the three pelagic fish species, herring, sprat and sandeel, contributed between 37% and 86% of the total fish biomass of the Moray Firth in June 1992, September/October 1993 and January 1994. The assemblage was dominated by the six most abundant species which accounted for 96% of the fish assemblage biomass in all three surveys. Two piscivorous fish species, whiting and haddock, were sufficiently abundant to have an impact on the pelagic fish prey resource. The percentage by weight of fish in the diets of both whiting and haddock increased with increasing predator length. Over 60% of the diet of whiting greater than 12 cm in length consisted of fish and little seasonal variation in this fraction was apparent. The percentage of fish in the diet of haddock was much lower and showed considerable seasonal variation. It exceeded 50% only in haddock of over 30 cm length, and only in June 1992 and January 1994. The piscivorous fraction of the whiting population biomass varied between 55% in September/October 1993 and 99% in June 1992. Only in June 1992 were haddock considered to be a serious predator of pelagic fish in the Moray Firth when 40% of the haddock biomass could be considered to be mainly piscivorous. The species composition of the fish fraction of the diets of both whiting and haddock showed considerable seasonal variation. For both predators it consisted almost exclusively of sandeels in June 1992 when the fish assemblage was dominated by sandeels. At other times, when sandeels were much less abundant in the water column and clupeids and gadoids more common, sprats were taken by the smaller whiting and haddock and small whiting by the larger predators. This difference in diet was attributed to larger predators being able to cope with larger prey.