Assessing bottom trawling impacts based on the longevity of benthic invertebrates

Abstract

1. Bottom trawling is the most widespread human activity directly affecting seabed habitats. Assessment and effective management of the effects of bottom trawling at the scale of fisheries requires an understanding of differences in sensitivity of biota to trawling. Responses to disturbance are expected to depend on the intrinsic rate of increase in populations (r), which is expected to be linearly related to the reciprocal of longevity. We examine the relationship between the longevity of benthic invertebrates andtheir response to bottom trawling; both in terms of the immediate mortality following a trawl pass and their subsequent rates of recovery. We collate all available data from experimental and comparative trawling studies, and test how longevity influences these aspects of sensitivity.3. The shortest lived organisms (<1 year) increased in abundance shortly after experimental trawling but showed no response to trawling in long-term comparative studies. Conversely, the abundance of biota with a life span >1 year decreased by ~9% immediately following a trawl pass. The effect of bottom trawling in comparative studies increased with longevity, with a 2-3× larger effect on biota living >10 years than on biota living 1-3 years. We attribute this difference to the slower recovery rates of the long-lived biota.4. The observed relationship between the intrinsic rate of population increase (r, our metric of recovery rate) and the reciprocal of longevity matches theoretical expectation and predicts that the sensitivity of habitats to bottom trawling is higher in habitats with higher proportions of long-lived organisms.

Recent advances in understanding the environmental footprint of trawling on the seabed

“…A further extension of this research has shown that taxon longevity predicts recovery rate (Rijnsdorp et al 2018;Hiddink et al 2019). The latter finding concurs with expectations based on our understanding of the likely response of long-lived species.…”

“…Some have rejected the notion that bottom trawling could ever be considered "sustainable" (Watling and Norse 1998). This debate highlights the need to better understand the resilience of habitats and communities to different levels of trawl activity with the goal of informing management and operational practices that might mitigate the effects of trawling on the seabed environment (e.g., Lambert et al 2014;Eigaard et al 2017;Pitcher et al 2017;Hiddink et al 2019). Irrespective of the philosophical considerations of what amount of trawling activity is, or is not, sustainable, there now exist numerous international and national policies that require the scientific community to assess the impacts of bottom fishing in relation to the maintenance of marine biodiversity, essential fish habitats, and other marine ecosystem processes (Friedman et al 2018).…”

Choosing best practices for managing impacts of trawl fishing on seabed habitats and biota

“…Brief examples and performance‐based analyses are used to develop guidance on best practices for a wide range of fisheries and associated management systems. Building on previous analyses of the impacts and management of trawling activities (Collie et al, ; Hiddink et al, , ; Pitcher et al, ; Sciberras et al, ), we address multiple knowledge gaps identified in a prioritization exercise concerned with reducing the environmental impacts of trawling (Kaiser et al, ). The resulting guidance on best practices is intended to help managers and the industry minimize environmental impacts of trawling per unit weight or value of landed fish, while achieving a sustainable level of fish production.…”

Impact of bottom trawling on sediment biogeochemistry: a modelling approach

“…The subsequent recovery of the bioturbation was modelled based on the logistic growth equation (Eq. 4), with the recovery rate (r) the inverse of the longevity of the species community, kept constant at 0.04 y -1 (Rijnsdorp et al, 2016;Hiddink et al, 2019).…”