# Substantial loss of trawlable biomass and lack of recovery in a marine ecosystem

## TL;DR

A long-term study shows a significant decline in trawlable marine biomass and little recovery in the Gulf of St. Lawrence ecosystem over 50 years.

## Contribution

The study reveals a unique case of substantial and persistent biomass loss following a regime shift in a marine ecosystem.

## Key findings

- Trawlable biomass in the southern Gulf of St. Lawrence declined significantly with increased species turnover.
- A regime shift in the early 1990s led to reduced predatory fish and limited recovery of small fish and crustaceans.
- Fishery-independent surveys highlight the importance of long-term data for understanding ecosystem changes.

## Abstract

Profound changes in species assemblages are occurring in marine ecosystems worldwide and are essential to document. Here we use 51 years (1971–2021) of fishery-independent data from a standardized bottom-trawl research vessel survey (6440 independent fishing locations) in the southern Gulf of St. Lawrence covering 70,091 km² to evaluate trends in marine community structure and trawlable biomass across 122 fish and crustacean taxa. Survey data indicate a substantial decline in biomass and increase in turnover for taxa susceptible to bottom-trawl fishing gear in the southern Gulf of St. Lawrence marine ecosystem that corresponds with the reduction of several predatory fish and a major regime shift around the early 1990’s. Unlike other marine regime shift examples, we observe a substantial net loss of trawlable biomass in the community, with limited compensatory response in small fish and crustacean biomass over nearly 30 years following the depletion of predatory groundfish. Overall, this unique case of reduced biomass and shift in community structure highlights the importance of maintaining and analyzing fishery-independent surveys over extended time series. Such information is vital to assessing the state of marine ecosystems and developing plans for recovery, as we face a future of untold challenges in managing marine ecosystems worldwide.

Analyses of a long term fishery-independent trawl survey dataset reveal substantial loss of trawlable biomass and shift in community structure in a marine ecosystem, with little signs of recovery.