First-Year Energy Storage Patterns of Pacific Herring and Walleye Pollock: Insight into Competitor Strategies

A.J. Paul, J.M. Paul
1999 Ecosystem Approaches for Fisheries Management   unpublished
Changes in length and whole body energy content for Pacific herring and walleye pollock from Prince William Sound, Alaska, were monitored in 1996 to describe growth patterns of these two pelagic competitors during their first year. Metamorphosed walleye pollock were first captured in June, when they averaged 34 mm in standard length (SL) and their whole body energy content (WBEC) was 2.7 kJ/g wet wt. In August they had grown to 69 mm and 3.4 kJ/g wet wt. In October they averaged 81 mm and 3.6
more » ... /g wet wt. Metamorphosed Pacific herring were first captured in July, and averaged 28 mm and 2.5 kJ/g wet wt. In August they had grown to 38 mm and 3.1 kJ/g wet wt. In October they averaged 75 mm and 5.0 kJ/g wet wt. Walleye pollock metamorphosed earlier than Pacific herring and in August and October they were on average 31 mm and 6 mm longer than their herring competitors. In August the WBEC of the two species was similar. In October the herring had stored on average ≈1.4 kJ/g more energy than pollock to enter the overwinter period. The survival strategy for first year pollock includes an early metamorphosis followed by rapid growth in length. For herring, metamorphosing later when conditions are warmer and storing more somatic energy for overwintering appear to be primary tactics. References Brodeur, R.D., and M.T. Wilson. 1996 A review of the distribution, ecology and population dynamics of age-0 walleye pollock in the Gulf of Alaska. Fish. Oceanogr. 5:148-166. Harris, R.K., T. Nishiyama, and A.J. Paul. 1986. Carbon, nitrogen and caloric content of eggs, larvae, and juveniles of the walleye pollock, Theragra chalcogramma. J. Fish Biol. 29:87-98. Hillgruber, N., L. Haldorson, and A.J. Paul. 1995. Feeding selectivity of larval walleye pollock Theragra chalcogramma in the oceanic domain of the Bering Sea. . 1993. Relationships between prey concentration and growth, condition and mortality of Pacific herring, Clupea pallasi, larvae in an Alaskan subarctic embayment. Can. Abstract Dramatic shifts in the species composition of the Georges Bank fish community have occurred during the past 30 years. The bottomfish community, once dominated by cod, haddock, and flounder, shifted to lower-value species such as skates and dogfish. Herring and mackerel declined during the 1960s and 1970s, but have since recovered to record levels. These shifts are attributed primarily to high fishing pressure, but predation is the largest source of pre-recruit mortality, and is also considered important in controlling the dynamics of the fish community. Prior studies have identified the important predators as cod, silver hake, and spiny dogfish. Herring, mackerel, silver hake, and yellowtail flounder all experience high predation mortality, especially in the first and second years of life. To construct dynamic production models of the Georges Bank fish community, we aggregated the dominant species into four groups: gadoids, flatfishes, pelagics, and elasmobranchs. Inclusion of species interactions in the dynamic models was based on statistical fits to the biomass data and groundtruthed with known species interactions. The most important interactions are predation of gadoids and elasmobranchs on pelagics and apparent competition between gadoids and elasmobranchs. Equilibrium yields of each group depend on the abundances and hence the exploitation rates of the other species. Harvest strategies are simulated for both the multispecies model and the corresponding single-species equations, to illustrate the sensitivity of medium-term projections to species interactions.
doi:10.4027/eafm.1999.12 fatcat:yawzz5tii5fo5hi7ot2zmeyfse