Hyperaggregation of fish and fisheries: how catch-per-unit-effort increased as the northern cod (Gadus morhua) declined

Abstract

Misinterpretations of elevated catch-per-unit-effort (CPUE) in the northern cod (Gadus morhua) fishery contributed to overestimations of stock size, inflated quotas, and unsustainable fishing mortality in the 1980s and early 1990s. We hypothesize that concentration of the fish and fishery led to extreme hyperstability in the CPUE-abundance relationship. In the late 1980s, migrant cod began to concentrate within the Bonavista corridor, their most southerly cross-shelf migration route. By the spring of 1990, approximately 450 000 t was concentrated within 7000 km2 at densities quadruple those of the 1980s. Densities remained high through 1992, while abundance declined fivefold. During this period, cod hyperaggregated (local densities increased with decreasing biomass) in the Bonavista corridor and CPUE increased. To the north, no hyperaggregation occurred, and densities and CPUE declined with biomass. In the Bonavista corridor from 1990 to 1993, CPUE was hyperstable with local cod density. Areas of high cod densities (>0.1 fish·m-2) shrunk as regional estimates of cod biomass declined. The spatial extent of the fishery contracted proportional to the shrinkage in area occupied by the fish. Hence, CPUE was related to abundance at the local scales of a fishing set (local acoustic density) but not to abundance at regional or stock scales.

Effects of a Severe Cold Event on the Subtropical, Estuarine-Dependent Common Snook, Centropomus undecimalis

“…Hyperstability occurs with fish that commonly aggregate, because an aggregation that is repeatedly targeted or sampled continues to result in high catches even though the overall abundance may have declined. The northern cod, Gadus morhua, fishery, for example, had an increasing catch-per-unit-effort while, in fact, the population was being overfished for decades (Rose and Kulka 1999) because of this bias. It is not possible to partition mortality and emigration in the calculation of apparent survival for this study, so we suggest two possible causes for the decline in common snook abundance on spawning grounds -lethal and sublethal effects.…”

Bayesian state-space models with multiple CPUE data: the case of a mullet fishery

“…This phenomenon, known as hyperstability, can misinform about the stock status. It becomes a risk for stock collapse in cases where the density of stock aggregation remains above the economic threshold (Rose andKulka 1999, Erisman et al 2011). It is important to consider that hyperstability may be occurring when M. liza stock is assessed.…”

Tracking Cairns: Biologging Improves the Use of Seabirds as Sentinels of the Sea

“…Food supply metrics, like population trends or relative abundance of seafood on different spatial scales, are often at the center of interest for fisheries management, and are typically quantified from commercial catch data. Yet those data can be biased, may miss early life stages that are important for predictive models, and will miss components of ecosystems that may be essential for ecosystem function but not commercially valuable (Richards and Schnute, 1986;Rose and Kulka, 1999;Salthaug and Godø, 2000). Ship-based biological surveys can provide additional data, but are expensive, especially in remote areas, such as the Arctic, and only cover a single trajectory and a single point in space at each time point (Montevecchi, 1993;Furness and Camphuysen, 1997).…”