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  • 1
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    Oxford Univ. Press
    In:  ICES Journal of Marine Science, 68 (5). pp. 813-822.
    Publication Date: 2019-09-23
    Description: In 1999, marine protected areas (MPAs) were implemented along the west coast of the Big Island of Hawaii, closing ~35% of the coastline to aquarium fishing. Catch per unit effort and total catch of the most commonly targeted fish, yellow tang (Zebrasoma flavescens), have increased since the implementation of the MPAs, yet its abundance has declined by 45% in areas open to aquarium fishing between 1999 and 2007. How effort allocation, harvesting efficiencies, and job satisfaction influence catch productivity and selectivity in West Hawaii’s aquarium fishery are investigated, and how these dynamics explain the discrepancy between catch rates and relative abundance for yellow tang is discussed. Cross-sectional fisher questionnaires, semi-structured fisher interviews, and in situ and ex situ catch analyses were performed. The results indicate that fishers dive deeper when reef fish recruitment is perceived as weak, increase harvest efficiency with larger fishing teams, and intensively harvest “coral-friendly” reef fish to supply the global aquarium fish trade. Experienced fishers were less likely to exit the fishery, and job satisfaction was high despite declining fish stocks. These findings may help explain harvesting efficiencies and fleet investment, underscore the importance for evaluating fisher behaviours, and have potential management implications for other aquarium fisheries.
    Type: Article , PeerReviewed
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  • 2
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    Oxford Univ. Press
    In:  ICES Journal of Marine Science, 68 (6). pp. 1244-1256.
    Publication Date: 2019-09-23
    Description: Temperature effects on Baltic sprat are many and include both direct and indirect effects. Increasing temperature is thought to increase the survival of all early life stages, resulting in increased recruitment success. We quantified the spatially resolved temperature trend for major spawning grounds and depth layers being most relevant for sprat eggs and larvae, using a three-dimensional hydrodynamic model for 1979–2005. Results confirmed an underlying positive temperature trend. Next, we tested these time-series as new explanatory variables in an existing temperature-dependent recruitment function and applied these recruitment predictions in an agestructured ecological–economic optimization model, maximizing for profit. Economic optimal solutions depended upon variability in temperature trajectories. Under climate-change scenarios, mean optimal fishing mortality and related yields and profits increased. The extent of the increase was limited by the general shape of the stock–recruitment model and the assumption of density-dependence. This highlights the need to formulate better environmentally sensitive stock recruitment models. Under the current knowledge of Baltic sprat recruitment, the tested climate-change scenarios would result in a change in management targets. However, to serve as a quantitative management advice tool, models will have to address the above-mentioned concerns
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 3
    Publication Date: 2019-09-23
    Description: To disentangle the effects of different drivers on recruitment variability of marine fish, a spatially and temporally explicit understanding of both the spawning stock size and the early life stage dynamics is required. The objectives of this study are to assess the transport of western Baltic cod early life stages as well as the variability in environmentally-mediated survival along drift routes in relation to both spatial (within and between different spawning areas) and temporal (interannual and seasonal) dynamics. A spatially and temporally highly-resolved biophysical model of the Baltic Sea was used to describe mortalities and survival success of eggs and yolk-sac larvae—represented by individual, virtual drifters—as predicted proportions of drifters that either died due to bottom contact or lethal temperatures, or that survived up to the end of the yolk-sac larval stage. The environmental conditions allowing survival of cod and yolk-sac larvae indicate that favourable conditions predominately occurred during the late spawning season, while minimum survival rates could be expected from January to March. The spatial analysis of different spawning areas revealed highest survival chances in the Kattegat, intermediate survival in the Great Belt, and only low survival in the Sound, Kiel Bay and Mecklenburg Bay.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 4
    Publication Date: 2018-02-27
    Description: Cod and sprat are the dominant fish species in the Baltic pelagic ecosystem, both of great economic importance and ecologically strongly interlinked. Management of both species is challenged by highly variable recruitment success. Recent studies have identified predation and hydrographic conditions during the egg phase to be of critical importance. Two years of extensive field investigations in the Bornholm Basin, central Baltic Sea, were undertaken. In 2002, a typical stagnation situation characterized by low salinity and poor oxygen conditions was investigated, and in early 2003, a major inflow of North Sea water completely changed the hydrographic conditions by increasing salinity and oxygen content, thereby altering ecological conditions. The goal was to quantify egg mortality caused by predation and hydrography, and to compare these estimates with independent estimates based on cohort analysis. Results indicated high intra-annual variability in egg mortality. Cod and sprat egg mortality responded differently to the major Baltic inflow: mortality related to hydrographic conditions increased for sprat and decreased for cod. On the other hand, predation mortality during peak spawning decreased for sprat and increased for cod.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 5
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    Oxford Univ. Press
    In:  ICES Journal of Marine Science, 71 (7). pp. 1876-1884.
    Publication Date: 2020-07-29
    Description: Species richness and abundance are two commonly measured parameters used to characterize invasion risk associated with transport vectors, especially those capable of transferring large species assemblages. Understanding the relationship between these two variables can further improve our ability to predict future invasions by identifying conditions where high-risk (i.e. species-rich or high abundance or both) and low-risk (i.e. species-poor and low abundance) introduction events are expected. While ballast water is one of the best characterized transport vectors of aquatic non-indigenous species, very few studies have assessed its magnitude at high latitudes. We assessed the arrival potential of zooplankton via ballast water in the Canadian Arctic by examining species richness, total abundance, and the relationship between the two parameters for zooplankton in ships from Europe destined for the Arctic, in comparison with the same parameters for ships bound for Atlantic Canada and the Great Lakes. In addition, we examined whether species richness and/or total abundance were influenced by temperature change and/or ballast water age for each shipping route. We found that species richness and total abundance for Arctic and Great Lakes ships were significantly lower than those for Atlantic ships. Differences in species richness and total abundance for ships utilizing different shipping routes were mostly related to ballast water age. A significant species richness–total abundance relationship for Arctic and Great Lakes ships suggests that these parameters decreased proportionately as ballast water aged. In contrast, the absence of such a relationship for Atlantic ships suggests that decreases in total abundance were accompanied by little to no reduction in species richness. Collectively, our results indicate that the arrival potential of zooplankton in ballast water of Arctic ships may be lower than or similar to that of Atlantic and Great Lakes ships, respectively.
    Type: Article , PeerReviewed
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