Density-dependent changes in the spatial distributions of Atlantic Cod (Gadus morhua), American Plaice (Hippoglossoides platessoides), and Greenland Halibut (Reinhardtius hippoglossoides) on the Flemish Cap during 1988-2002

Abstract

The Flemish Cap is an isolated bank located east of the Grand Banks in the Northwest Atlantic Ocean. Research bottom trawl surveys of the Flemish Cap have been conducted in July by the European Union since 1988. Data from these surveys were used to assess changes in the spatial distributions of Atlantic cod (Gadus morhua), American plaice (Hippoglossoides platessoides), and Greenland halibut (Reinhardtius hippoglossoides) during 1988-2002. Kriging and indices of collocation and co-occurrence indicated that cod and plaice distributions have a high degree of overlap and that density-dependent range contraction of both stocks occurred during a time when Greenland halibut, a more common inhabitant of deep water, exhibited range expansion into shallow water on the Cap. However, the timing and locations of these distributional changes were such that little overlap occurred between the distributions of Greenland halibut and either cod or plaice. The range expansion of Greenland halibut was also density-dependent and primarily attributable to young fish (ages 1 and 2 from the 1994 and 1995 year-classes) which prefer shallow water. The range contractions of cod and plaice have persisted since the mid-1990s, and despite fishing moratoria implemented for plaice in 1994 and for cod in 1999, neither stock has shown signs of recovery. Biological and stock assessment implications of these distribution changes are discussed in relation to the lack of recovery.

Relative importance of population size, fishing pressure and temperature on the spatial distribution of nine Northwest Atlantic groundfish stocks

“…Biomass was the most important predictor of area occupancy for both cod stocks, southern silver hake, and both yellowtail flounder stocks in spring and fall. This confirms previous analyses that have shown similar relationships for cod and yellowtail flounder in Canadian waters [ 47 – 49 ], as well as cod, American plaice ( Hippoglossoides platessoides ) and Greenland halibut ( Reinhardtius hippoglossoides ) on the Flemish Cap [ 50 ]. All of these findings comport with a recent analysis of six marine regions around the world which found that abundance-area occupancy relationships are strongest for Gadiformes, followed by Pleuronectiformes [ 51 ].…”

Using global catch data for inferences on the world’s marine fisheries

“…Catches will eventually also decrease, although they may lag behind in the case of concentrated fishing pressure on a range‐contracting species (e.g. Atlantic cod; Rose and Kulka 1999; Hendrickson and Vazquez 2005; Wilberg et al. 2010).…”

Demersal groundfish assemblages and depth-related trends on Flemish Cap (NAFO division 3M): 2004–2013

“…But our analysis shows that American plaice has returned to their pre-collapse distribution and are again found in waters less than 480 m. Greenland halibut also shifted its depth distribution potentially in response to declines in cod abundance. During the period 1988-2002, Greenland halibut moved into shallower waters and became more abundant at depths of 256-549 m than 549-730 m, and Paz and Casas (1996) and González-Troncoso et al (2006) found this species in the upper slope assemblage with median depth less than 500 m. This range of expansion into shallower waters can be attributed to an increased abundance of small fish, that inhabits at less depth (Hendrickson and Vázquez, 2005;Alpoim and Ávila de Melo, 2004). Thus, Greenland Halibut extended its range to shallower waters previously inhabited by cod and American plaice, both significant predators, when these species were collapsed (Hendrickson and Vázquez, 2005).…”