Change in habitat associations and geographic distribution of thorny skate (Amblyraja radiata) in the southern Gulf of St Lawrence: density‐dependent habitat selection or response to environmental change?

Abstract

We describe changes in the habitat associations and geographic distribution of thorny skate during their feeding season in the southern Gulf of St Lawrence, based on 32 yr of monitoring by a bottom-trawl survey. In the 1990s, geographic range contracted sharply and distribution shifted into a narrow band of warm deep waters. These changes appeared to reflect altered habitat selection by individual skates, rather than local depletion of the skates that had habitually occupied the vacated areas or a change in the timing of seasonal migrations. Changes in skate distribution coincided with a decline in skate biomass and a cooling of bottom waters. The contraction in the geographic range of skates appeared to be a densitydependent response, more closely linked to the decline in skate abundance than to the change in environmental conditions. The cause of the shift in habitat associations is less certain. An index of the distribution shift was more strongly correlated with skate biomass than with an index of temperature conditions, and the change in temperature associations is in the direction predicted by density-dependent bioenergetic considerations. However, the shift into deeper waters is into a depth zone where skate condition is relatively low, contrary to the expectation that fish should be concentrated in optimal habitat at low population size. On the other hand, while the shift into warm deep waters coincided with a cooling of waters at intermediate depths, distribution failed to shift back to the earlier pattern as these waters warmed in the late 1990s.

Trophic Resource Overlap Between Small Elasmobranchs and Sympatric Teleosts in Mid-Atlantic Bight Nearshore Habitats

“…(2) competitive release due to large-scale fishery removals of sympatric groundfish species (Fogarty and Murawski 1998); (3) metapopulation dynamics associated with oceanic regime shifts (Frisk et al 2008); (4) bycatch reduction in coastal trawl fisheries (Brewer et al 1998); and (5) density-dependent habitat selection (Swain and Benoit 2006). Regardless of the cause(s), this potential shift in community structure has raised concerns about the effects on local food web dynamics and the recovery and productivity of economically valuable species (Fogarty and Murawski 1998;Myers et al 2007).…”

Fine-scale analysis of arrowtooth flounder Atherestes stomias catch rates reveals spatial trends in abundance

“…Community-wide northward distribution shifts of fish and invertebrates in the EBS have been linked in part to the northward retreat of the cold pool (Mueter & Litzow 2008). Shifts in geographic distributions of other groundfish have been more closely linked to density-dependent processes rather than changes in environmental conditions (Swain & Wade 1993, Swain & Benoit 2006. Indeed, arrowtooth population expansion to the middle of the EBS shelf was demonstrated to occur with increases in abundance, suggesting density-dependent habitat selection, but this shift was found to be more strongly related to the reduction in the cold pool during warm years (Spencer 2008).…”

Reproductive biology of the Japanese mantis shrimpOratosquilla oratoria(Crustacea Stomatopoda): Annual cycle of gonadal development and copulation

“…In general, the spatial distribution of fished species is density-dependent; expansion of the habitat range at high density and contraction at low density have been recognized in a number of species (e.g. Gadus morhua Linnaeus, 1758 [Swain & Wade 1993]; Callinectes sapidus Rathbun, 1896 [Jensen & Miller 2005]; Amblyraja radiata (Donovan, 1808) [Swain & Benoit 2006]). The stock size of O. oratoria in Tokyo Bay decreased abruptly in 2005 (Kodama et al 2009), which may have led to a contraction of the spatial distribution, and thus to decreased abundance around the sampling sites.…”