Top-down interactions and temperature control of snow crab abundance in the northwest Atlantic Ocean

Abstract

In much of the northwest Atlantic Ocean, commercially important snow crab Chionoecetes opilio stocks have increased in abundance since the decline and collapse of major groundfish stocks such as Atlantic cod Gadus morhua. We examined 3 hypotheses to explain variation in the abundance of snow crabs across 10 regions: (1) climate control of both species, (2) top-down control of snow crab by cod and (3) bottom-up control of cod by snow crab. We tested these hypotheses by analyzing time series data of cod and crab abundance indices and temperature via meta-analysis of full and partial correlation coefficients. We found that temperature had an opposing effect on the 2 species: snow crab abundance was negatively correlated with temperature at 7 to 10 yr lags, whereas cod and temperature were positively related at 1 to 7 yr lags. Controlling for the effect of temperature, our meta-analysis revealed significant negative correlations of snow crab and cod abundance, with cod leading snow crab by up to a 5 yr lag. This suggests a top-down effect on older juvenile and subadult snow crab. We found no evidence of a bottom-up effect of snow crab on cod. Negative correlations between cod and crab abundance were observed both at the warmer and colder portions of their ranges. These results suggest that snow crab abundance is largely influenced by temperature during the early postsettlement years and becomes increasingly regulated by top-down mechanisms during the years approaching fishery recruitment. The method presented in this paper is generally useful to test ecological hypotheses from time series data, particularly where multiple causal mechanisms are suspected.

Ecological role of large benthic decapods in marine ecosystems: a review

“…A similar release from (mostly gadoid) fish predation has contributed to observed increases in the abundance of American lobster and snow crab in the NW Atlantic (e.g. Worm & Myers 2003, Steneck et al 2004, Frank et al 2005, Zhang & Chen 2007, Boudreau & Worm 2010, Boudreau et al 2011). This body of evidence adds to a growing concern that commercial fisheries have the potential to affect ecosystem function through the removal of certain predators (Fig.…”

“…As more decapod populations are of increasing socio-economic importance and continue to be harvested more widely (Anderson et al 2011), it is important that we expand our knowledge of ecological interactions that affect the abundance of these species, their prey, and habitat. It is our hope that this knowledge may ultimately help managers maintain critical trophic interactions and prevent overexploitation in an ecosystem context.…”

“…Moss 1972, Robichaud et al 1991, Rountree & Able 1996, Steneck 1997, Boudreau & Worm 2010, Boudreau et al 2011. Some predators may be more important than others; in the soft substrates of the Southern Gulf of St. Lawrence, the shorthorn sculpin Myoxocephalus scorpius was the only demersal fish to consume large amounts of American lobsters (2.6% frequency of occurrence, 28.9% biomass).…”

“…Large crustaceans are becoming increasingly important to coastal and continental shelf fisheries (Anderson et al 2011, Steneck et al 2011. For example, in eastern North America, a well-documented shift has occurred from groundfish, such as Atlantic cod Gadus morhua, to invertebrates that now dominate commercial landings and value (Worm & Myers 2003, Frank et al 2005.…”

“…For example, in eastern North America, a well-documented shift has occurred from groundfish, such as Atlantic cod Gadus morhua, to invertebrates that now dominate commercial landings and value (Worm & Myers 2003, Frank et al 2005. Globally, commercial catches of crustaceans have increased ~5-fold since 1950 and are the only invertebrate group that continues to trend upward in recent years (Anderson et al 2011). Yet, when compared to finfish, there is a much smaller knowledge base available from which to manage these fisheries, particularly in an ecosystem context (Anderson et al 2008).…”