ICES Journal of Marine Science: Journal du Conseil

Delfour-Samama, Odile; Leboeuf, Cédric

doi: 10.1093/icesjms/fsu024pmid: N/A

Marine protected areas (MPAs) were initially introduced to protect coastal zones and are increasingly being proposed as part of a solution to an integrated approach in managing the oceans. There is also pressure for the use of marine reserves to play a part in the conservation strategy and management of mobile demersal and pelagic species in the high seas. However, as there is no coastal State, all States are free to use the open seas, and the relative success of MPAs depends on whether or not measures can be imposed on both domestic and foreign vessels. Therefore, the question is whether current international and national legislation is sufficiently effective to implement a solution to aid the success of MPAs or if new legal norms need to be introduced to aid the governance of the high seas. The implementation of a surveillance programme of maritime spaces would help to establish the efficacy of any review of the current legislation. New technical developments being utilized in surveillance have opened up the possibility of exploiting technology with a view to surveying and monitoring planet earth in an objective manner. But technical applications employed to manage risks can themselves be dangerous, as they create new risks for the maritime sector (e.g. espionnage). The maritime domain is a difficult and unpredictable environment in which to operate and, therefore, precludes the assured presence of human beings to perform monitoring tasks. Technology offers us the opportunity to overcome the physical difficulties by putting into practice surveillance using more effective methods. Identifying the appropriate technology and providing funding is a priority.

Hilborn, Ray; Ovando, Daniel

doi: 10.1093/icesjms/fsu034pmid: N/A

The argument persists that the continued overexploitation by many fisheries around the world is evidence that current approaches to fisheries management are failing, and that more precautionary management approaches are needed. We review the available estimates of the status of fish stocks from three sources: the FAO's “State of Marine Resources”, a database on scientific stock assessments, and recent estimates from statistical models designed to determine the status of unassessed fish stocks. The two key results are (i) that stocks that are scientifically assessed are in better shape and indeed are not typically declining but rebuilding, and (ii) that large stocks appear to be in better shape than small stocks. These results support the view that stocks that are managed are improving, while stocks that are not managed are not. Large stocks receive far more management attention than small stocks in jurisdictions that have active fisheries management systems, and most unassessed stocks are simply not managed. We assert that fisheries management as currently practised can (and often does) lead to sustainable fisheries, and what is needed is to actively manage the unassessed fisheries of the world. More precautionary management is not necessarily needed to ensure the sustainability of managed fisheries.

Ciannelli, Lorenzo; Hunsicker, Mary; Beaudreau, Anne; Bailey, Kevin; Crowder, Larry B.; Finley, Carmel; Webb, Colleen; Reynolds, John; Sagmiller, Kay; Anderies, John M.; Hawthorne, David; Parrish, Julia; Heppell, Selina; Conway, Flaxen; Chigbu, Paulinus

de Lestang, Simon

doi: 10.1093/icesjms/fst205pmid: N/A

Large-scale migrations are known to occur in numerous species, and in the case of the Western Rock Lobster, Panulirus cygnus, result in juveniles moving from nursery areas into deeper offshore breeding grounds. In 2008 the Western Rock Lobster fishery reduced harvest rates to increase legal and spawning biomass throughout the fishery, which also allowed greater numbers of lobsters to migrate. Increased lobster migration could potentially reduce biomass in some areas, thus adversely impacting commercial catch rates. Over 20 000 tag–recaptured lobsters were analysed to determine the dynamics underlying migration in this species and to assess the impact reduced harvest rates may have had on catches. This study showed that P. cygnus migration was associated with body size and water depth, and that magnetism and oceanic currents appear to be the most likely guideposts used for orientation. Size at migration varied in a constant fashion along the coast, being larger towards the southern end of the fishery and smallest at the offshore Abrolhos Islands. During the migration period, up to 50% of lobsters at their mean size of migration moved from coastal areas out towards deeper waters (>40 m), whereas <15% of those in deeper water at the same size moved significant distances northward. This behaviour appears to be contranatant, counteracting the downstream redistribution of larvae after their 9–11 month larval life. Reduced harvest rates and catches being focussed onto higher valued sedentary lobsters have allowed more lobsters to migrate. However, the numbers moving between management areas are relatively small, with the biological and economic benefits of fishing at a reduced exploitation rate outweighing losses to catches.

Ouréns, Rosana; Freire, Juan; Vilar, Jose A.; Fernández, Luis

doi: 10.1093/icesjms/fst201pmid: N/A

We studied the spatial variation in recruitment and the population dynamics of the sea urchin Paracentrotus lividus, analysing the effect of depth and presence of sea urchin aggregations on population structure. Over 90% of the observed recruits (individuals under 1 year of age) were concentrated in aggregations found in shallow waters. In these areas, a positive linear relationship was found between adult and recruit density, possibly due to higher survival rates of juveniles taking refuge among the spines of adults. The scarcity of recruits and the presence of adult sea urchins at depths of 8 and 12 m suggest the migration of part of the population towards deep areas when individuals reach a size of ∼40 mm. In light of these results, the implementation of harvest refugia for sea urchins in shallow areas could constitute an effective fishery management tool for this species. High population densities could enhance recruitment, given the inverse density dependence of this process, while their migratory pattern would guarantee biomass exportation towards deeper fishing grounds.

Chouvelon, T.; Caurant, F.; Cherel, Y.; Simon-Bouhet, B.; Spitz, J.; Bustamante, P.

doi: 10.1093/icesjms/fst199pmid: N/A

Recent European environmental policies argue for the development of indicators of the ecological status of ecosystems that are easy to implement and powerful enough to detect changes quickly. For instance, some indicators that are currently proposed for monitoring foodweb structure and functioning are based on the size of organisms, using size as a proxy for trophic level. However, these indicators do not necessarily accurately reflect the underlying trophic structure and dynamics to follow. Ecological tracers (i.e. chemical parameters measured in consumer tissues to infer the trophic ecology of organisms) may serve as complementary indicators of trophic level, and may also help distinguish different populations of a species when more commonly used methods (e.g. genetic, age determination) present their own limitations. Here, we analysed the potential of muscle δ13C and δ15N values and of muscle mercury (Hg) concentrations to depict size-related trophic habits of different fish species. We expected that intra- and interspecific variation in these ecological tracers could be helpful in refining currently proposed indicators of marine ecosystems, and also help in discriminating management unitsfor some species. Four fish species were selected for their economical and/or ecological importance in the Bay of Biscay (Northeast Atlantic): whiting Merlangius merlangus, European hake Merluccius merluccius, Atlantic horse mackerel Trachurus trachurus and anglerfish Lophius piscatorius. Muscle δ13C and δ15N values segregated the species and enabled us to discriminate species-specific feeding strategies with increasing size of individuals. Fish body size was not always linearly correlated with δ15N or trophic level. In contrast, Hg concentrations and size-related Hg patterns were more similar from species to species. Interestingly, muscle δ15N values together with Hg concentrations segregated the two putative stocks of European hake within the Bay of Biscay. Hence, we propose the combined use of ecological tracers as a promising method for accurately assigning a consumer to a trophic guild, investigating Hg trophodynamics in foodwebs, and helping discriminate distinct ecological populations within a species when defining management units.

Ferrer-Maza, Dolors; Lloret, Josep; Muñoz, Marta; Faliex, Elisabeth; Vila, Sílvia; Sasal, Pierre

doi: 10.1093/icesjms/fst217pmid: N/A

It is well known that parameters relating to physical condition and reproduction of fish provide essential data for estimating the productivity of exploited populations, as is the case with the European hake (Merluccius merluccius) in the northwestern Mediterranean Sea. Although parasitism might affect these parameters, research in this area is very scarce (and in the case of the Mediterranean almost non-existent). This study evaluates for the first time the potential link between parasitism, condition and reproduction of the European hake. Indicators of fish energy reserves (total lipid content in liver and gonads) and reproductive capacity (fecundity, egg quality and atresia) were evaluated, as were the prevalence and intensity of infection by metazoan parasites. The results indicate that the impact of anisakid nematodes is mostly negative and occurs mainly when hake are allocating their energy reserves to gonadal development. Although the results reveal a link between parasitism, condition and reproduction, we concluded that the northwestern Mediterranean hake population is in equilibrium with its metazoan parasites, which are not causing severe impairment to their physical condition or reproductive capacity.

Pursche, Alexander R.; Suthers, Iain M.; Taylor, Matthew D.

doi: 10.1093/icesjms/fst209pmid: N/A

Targeted stocking involves the release of fish directly into high-quality habitat, however this is often time-consuming, expensive and difficult. Acoustically tagged hatchery-reared juvenile mulloway Argyrosomus japonicus were released in groups directly into deep-hole habitat preferred by wild conspecifics (targeted stocking), or in a non-targeted fashion near easily accessible sites that lacked high-quality habitats in the direct vicinity. Fish were tracked continuously, 24 h d−1, for 5 d following release. Fish released in a targeted fashion showed lower mean activity rates (50% less movement) and occupied higher quality habitats than fish released in a non-targeted fashion. Fish released in a non-targeted fashion also used a greater number of smaller habitat patches. The implications for improvements in behaviour and habitat usage patterns for fish released in a targeted fashion, such as improved growth and survival, are discussed. Identifying and releasing fish directly into the species' high-quality habitat may ultimately improve the success of stocking programs.

Kotwicki, Stan; Ianelli, James N.; Punt, André E.

doi: 10.1093/icesjms/fst208pmid: N/A

Indices of abundance are important for estimating population trends in stock assessment and ideally should be based on fishery-independent surveys to avoid problems associated with the hyperstability of the commercial catch per unit effort (cpue) data. However, recent studies indicate that the efficiency of the survey bottom trawl (BT) for some species can be density-dependent, which could affect the reliability of survey-derived indices of abundance. A function qe∼f(u), where qe is the BT efficiency and u the catch rate, was derived using experimentally derived acoustic dead-zone correction and BT efficiency parameters obtained from combining a subset of BT catch data with synchronously collected acoustic data from walleye pollock (Theragra chalcogramma) in the eastern Bering Sea (EBS). We found that qe decreased with increasing BT catches resulting in hyperstability of the index of abundance derived from BT survey. Density-dependent qe resulted in spatially and temporarily variable bias in survey cpue and biased population age structure derived from survey data. We used the relationship qe∼f(u) to correct the EBS trawl survey index of abundance for density-dependence. We also obtained a variance–covariance matrix for a new index that accounted for sampling variability and the uncertainty associated with the qe. We found that incorporating estimates of the new index of abundance changed outputs from the walleye pollock stock assessment model. Although changes were minor, we advocate incorporating estimates of density-dependent qe into the walleye pollock stock assessment as a precautionary measure that should be undertaken to avoid negative consequences of the density-dependent qe.

Thorson, James T.

doi: 10.1093/icesjms/fst224pmid: N/A

Stock assessment models frequently integrate abundance index and compositional (e.g. age, length, sex) data. Abundance indices are generally estimated using index standardization models, which provide estimates of index standard errors while accounting for: (i) differences in sampling intensity spatially or over time; (ii) non-independence of available data; and (iii) the effect of covariates. However, compositional data are not generally processed using a standardization model, so effective sample size is not routinely estimated and these three issues are unresolved. I therefore propose a computationally simple “normal approximation” method for standardizing compositional data and compare this with design-based and Dirichlet-multinomial (D-M) methods for analysing compositional data. Using simulated data from a population with multiple spatial strata, heterogeneity within strata, differences in sampling intensity, and additional overdispersion, I show that the normal-approximation method provided unbiased estimates of abundance-at-age and estimates of effective sample size that are consistent with the imprecision of these estimates. A conventional design-based method also produced unbiased age compositions estimates but no estimate of effective sample size. The D-M failed to account for known differences in sampling intensity (the proportion of catch for each fishing trip that is sampled for age) and hence provides biased estimates when sampling intensity is correlated with variation in abundance-at-age data. I end by discussing uses for “composition-standardization models” and propose that future research develop methods to impute compositional data in strata with missing data.