An Ecosystem Approach for Assessment Advice and Biological Reference Points for the Gulf of Maine–Georges Bank Atlantic Herring Complex

Abstract

The biomass of Atlantic herring Clupea harengus in the Gulf of Maine–Georges Bank (GOM–GB) region declined sharply in the mid- to late 1970s, when fishery harvests ranged from 300 to 400 kilo–metric tons (kt) per year. During this same period, the consumption of Atlantic herring by fish and marine mammal predators was very large. Consumption has greatly exceeded landings from 1985 to the present. Previous research showed that four groups of predators (demersal fishes, marine mammals, large pelagic fishes, and seabirds) together annually consumed over 200 kt of Atlantic herring during the 1970s and over 300 kt during the late 1990s and early 2000s. Our analyses indicate that Atlantic herring predation mortality rates are related to the abundance of both Atlantic herring and predators. Predation mortality rates were relatively low during the 1960s, when Atlantic herring were abundant, but increased in the late 1970s and early 1980s, when Atlantic herring declined. Predation mortality rates declined in the 1990s as Atlantic herring abundance increased. Biological reference points for the Atlantic herring complex (composed of two stocks) are significantly different when predation mortality is included. Several methods were used to assess the available fishery yield given that predator requirements have first been satisfied. In general, all of the approaches indicated that the maximum sustainable yield harvest level for the GOM–GB Atlantic herring complex is lower than that estimated from the single-species assessment in which predation effects are not explicitly accounted for.