Mitigating unaccounted fishing mortality from gillnets and traps

Abstract

Gillnets and traps often are considered to have fewer holistic environmental impacts than active fishing gears. However, in addition to the targeted catches, gillnets and traps still cause unwanted mortalities due to (i) discarding, (ii) ghost fishing of derelict gear, (iii) depredation, (iv) escaping or dropping out of gear, (v) habitat damage, and potentially (vi) avoiding gear and predation and (vii) infection of injuries sustained from most of the above. Population‐level concerns associated with such ‘unaccounted fishing mortalities’ from gillnets and traps have been sufficient to warrant numerous attempts at mitigation. In this article, we reviewed relevant research efforts, locating 130 studies in the primary literature that concomitantly quantified mortalities and their resolution through technical modifications, with the division of effort indicating ongoing concerns. Most studies (85) have focused on discard mortality, followed by ghost‐fishing (24), depredation (10) and escape (8) mortalities. The remaining components have been poorly studied (3). All problematic mortality components are affected by key biological (e.g. species), technical (e.g. fishing mechanisms) and/or environmental (e.g. temperature) factors. We propose that these key factors should be considered as part of a strategy to reduce impacts of these gears by first assessing modifications within and then beyond conventional configurations, followed by changes to operational and handling practices. Justification for this three‐tiered approach is based not only on the potential for cumulative reduction benefits, but also on the likely ease of adoption, legislation and compliance.

Status of international monitoring and management of abandoned, lost and discarded fishing gear and ghost fishing

“…For instance, ALDFG and other marine debris transport invasive alien species, which can disrupt community structure and processes [4,13,52,53]. Organisms entangled in ALDFG may experience sublethal effects, such as reduced mobility and concomitant compromised ability to forage and avoid predators, which might eventually lead to the organism's demise [5,24,40,54]. ALDFG may be located in critical habitat where it poses a hazard to wildlife, including in foraging areas, fish spawning grounds, turtle nesting areas and migration routes [37].…”

Exploring Causal Factors of Spawning Stock Mortality in a Riverine Striped Bass Population

“…This suggests that the commercial multispecies gill-net fishery imparts substantial mortality even when the Striped Bass harvest season is closed. The reason for this mortality is obscure, but it may be attributable to dead discard mortality; over-quota and high-grading mortality; avoidance, predation, and drop-out mortality; or unreported, misreported, and illegal harvest (ICES 1995;Gilman et al 2013;Batsleer et al 2015;Uhlmann and Broadhurst 2015). In particular, discard mortality should be carefully considered, as Clark and Kahn (2009) found that Striped Bass are acutely susceptible to discard mortality in multispecies gill-net fisheries.…”

Post-Capture Survival and Implications for By-Catch in a Multi-Species Coastal Gillnet Fishery

“…Mortalities were recorded and removed from the tanks. This period of time is commonly used in post-capture survival studies [12,13,26,27] since the majority of capture-induced mortalities tend to occur relatively soon after capture and longer holding periods risk introducing confounding factors arising from confinement.…”

“…In a major review of fishing mortality mitigation by entangling and entrapment fishing gears, only 11 out of 130 primary literature sources examined estimated post-capture survival of fish by-catch [12]. While we are aware of two additional studies relevant to the post-capture survival of fish taken by gillnetting [13,14], there remains a paucity of information on this issue.…”