Capelin

Abstract: A shift in ocean climate during the late 1970s triggered a reorganization of community structure in the Gulf of Alaska ecosystem, as evidenced in changing catch composi- tion on long-term (1953-1997) small-mesh trawl surveys. Forage species such as pandalid shrimp and capelin declined because of recruitment failure and predation, and populations have not yet recovered. Total trawl catch biomass declined > 50% and remained low through the 1980s. In contrast, recruitment of high trophic-level groundfish improved during the 1980s, yielding a > 250% increase in catch biomass during the 1990s. This trophic reorganization apparently had negative effects on piscivorus sea birds and marine mammals.

Abstract: This review provides an overview of prey preferences of seven core Arctic marine mammal species (AMM) and four non-core species on a pan-Arctic scale with regional examples. Arctic marine mammal species exploit prey resources close to the sea ice, in the water column, and at the sea floor, including lipid-rich pelagic and benthic crustaceans and pelagic and ice-associated schooling fishes such as capelin and Arctic cod. Prey preferred by individual species range from cephalopods and benthic bivalves to Greenland halibut. A few AMM are very prey-, habitat-, and/or depth-specific (e.g., walrus, polar bear), while others are rather opportunistic and, therefore, likely less vulnerable to change (e.g., beluga, bearded seal). In the second section, we review prey distribution patterns and current biomass hotspots in the three major physical realms (sea ice, water column, and seafloor), highlighting relations to environmental parameters such as advection patterns and the sea ice regime. The third part of the contribution presents examples of documented changes in AMM prey distribution and biomass and, subsequently, suggests three potential scenarios of large-scale biotic change, based on published observations and predictions of environmental change. These scenarios discuss (1) increased pelagic primary and, hence, secondary production, particularly in the central Arctic, during open-water conditions in the summer (based on surplus nutrients currently unutilized); (2) reduced benthic and pelagic biomass in coastal/shelf areas (due to increased river runoff and, hence, changed salinity and turbidity conditions); and (3) increased pelagic grazing and recycling in open-water conditions at the expense of the current tight benthic-pelagic coupling in part of the ice-covered shelf regions (due to increased pelagic consumption vs. vertical flux). Should those scenarios hold true, pelagic-feeding and generalist AMM might be advantaged, while the range for benthic shelf-feeding, ice-dependent AMM such as walrus would decrease. New pelagic feeding grounds may open up to AMM and subarctic marine mammal species in the High Arctic basins while nearshore waters might provide less abundant food in the future.

Abstract: SYNOPSIS. We examine the variation in egg sizes of marine teleosts and evaluate the maternal contribution to this variability. At the species level, egg sizes in 309 North Atlantic fishes range from 0.3 to 18.0 mm diameter (median = 1.1), size at hatching varies directly with egg size, and large adult size is associated with large eggs but the relationship is weak. Within populations, egg sizes are distributed normally with a median coefficient of variation of 4% (n = 56 species). Egg size varied among females in all cases for which female-level data were found. Estimates of the variance components of egg size due to females were found for three species and, as a percentage of total variance, are 71 % for capelin, Mallotus villosus , 46% for winter flounder, Pleuronectes americanus , and 35% for Atlantic cod, Gadus morhua . For cod, which spawn multiple egg batches per year, an additional batches-within-females component was estimated to be 26%. Size at hatching also differs among sibgroups and is generally directly related to egg size at the individual level. We modelled fish growth by allowing individuals to grow at exponential rates from a normal distribution of initial sizes. Comparing size variation in model fish to empirical evidence suggests that variation in initial sizes, propagated by growth, could account for a large fraction of the size variation observed months after hatching in natural populations. We view size variation in young marine fishes to be largely of maternal origin and environmentally modulated, which if true has special consequences for fisheries and aquaculture.