Fish community structure and the spatial and temporal variability in recruitment and biomass production in Chesapeake Bay.

摘要

Spatio-temporal variability in community structure, recruitment and production of pelagic and bentho-pelagic fishes were investigated from 1995 to 2000 based on seasonal midwater trawl collections throughout Chesapeake Bay. Freshwater input and dissolved oxygen level were major physical forces controlling fish community structure. A correspondence analysis indicated that fish community structure was altered dramatically in 1996 by high freshwater flow and then restored progressively towards ‘normal’ in 1997–2000. In ‘normal’ years (1995, and 1997–2000), bay anchovy Anchoa mitchilli and Atlantic croaker Micropognias undulatus dominated fish biomass, but anadromous species such as white perch Morone americana and young-of-the-year alosids Alosa spp. dominated in 1996. Fish biomass size spectra were consistently bimodal. Bay anchovy is the key species in the smaller fish group (first dome) throughout the Bay whereas white perch in the upper Bay and Atlantic croaker in the lower Bay were key species in the larger fish group (second dome). High productivity of bay anchovy and bentho-pelagic coupling were hypothesized to explain unexpectedly high biomass of the larger fish group. In the middle Bay, where mean depth was greatest and episodic hypoxia was common, the fish community had low diversity, a probable consequence of weak bentho-pelagic coupling. Averaged dissolved oxygen level, a possible indicator of planktonic and benthic invertebrate productivity, was negatively correlated with overall annual fish production. Averaged dissolved oxygen level also was related to location of spawning stock biomass distribution and subsequent recruitment level of bay anchovy. The stock-recruitment relationship of bay anchovy was density-compensatory. The increasing dominance and contribution of young-of-the-year (YOY) fishes to overall fish biomass from spring to fall in each year illustrated the Bay's important nursery function. Fish productivity, especially by YOY bay anchovy, is high compared to other estuarine systems. Mean production of YOY bay anchovy from 1995–2000, based on a single-species allometric model, was 311 × 103 tons = 9.5 g C m−2 yr −1. This estimate was 3 times higher than one derived from a multispecies size-spectrum model. Estimated mean annual pelagic fish production, mostly excluding Atlantic menhaden Brevoortia tyrannus, was 408 × 103 tons = 11.4 g C m−2 yr −1.