Inter‐ and intra‐specific interactions affecting crustacean trap fisheries—Implications for management

Abstract

The UK coastal trap fisheries target two key species, European lobster Homarus gammarus (L.) and brown crab Cancer pagurus L. Their stock status is assessed periodically using size‐based, yield‐per‐recruit analysis. Fishery trends are described using landings and, where available, effort data to estimate catch per unit of effort (CPUE), nominally proportional to abundance. Despite being caught together, assessments assume that concurrent capture of these species does not distort their individual CPUE estimates. Here, an in situ experiment tested impacts of inter‐specific and intra‐specific interactions by pre‐loading baited traps with different species and observing subsequent catches. Pre‐loaded European lobster significantly reduced brown crab catches, whereas, other species produced no such effects. The findings highlight the likely inconsistency of using CPUE as an index of abundance if landings data originate from a mixed‐species fishery in which species interactions and targeting behaviour of fishers are unknown or un‐quantified.

Enhancing fishery-dependent information in data-poor fisheries; integrating gear-in–gear-out sensors and mobile reporting technology in a mixed Irish Sea static-gear fishery

“…Active targeting behaviour by fishers occurs between target species, i.e. Bait type and/or spatial distribution of fishing activity mirroring species-specific preferential habitat (Skerritt et al, 2020). The targeted IoM crab fishery typically occurs outside of the 1 nm limit, on sandy to mud substrate at depths ≥25 m. Conversely, the targeted lobster fishery occurs primarily within the 1nm limit, typically at depths ≈20 m on rocky/sublittoral reef habitats (Emmerson, person obv).…”

“…However, there are a number of methodological concerns associated with the use of fisheries-dependent LPUE as a BRP in static gear fisheries (e.g. green crab Carcinus maenas-Murray and Seed 2010; king scallop Pecten maximus- Murray et al (2013); brown crab C. pagurus; and European lobster H. gammarus- Skerritt et al 2020), as well as underlying issues of data resolution, precision, and accuracy of reporting systems. These concerns relate to the effect of both environmental and biotic factors affecting overall catchability and interaction of the target species with the fishery/gear, such as inter-and intra-specific interactions (Skerritt et al, 2020), bait attraction (McQuinn et al, 1988), temperature (Lizárraga-Cubedo et al, 2015;Mullowney, 2016;Bakke et al, 2019), soak time (Bennett, 1974), and fisher targeting behaviours and associated local ecological knowledge (Santos et al, 2019).…”

“…green crab Carcinus maenas-Murray and Seed 2010; king scallop Pecten maximus- Murray et al (2013); brown crab C. pagurus; and European lobster H. gammarus- Skerritt et al 2020), as well as underlying issues of data resolution, precision, and accuracy of reporting systems. These concerns relate to the effect of both environmental and biotic factors affecting overall catchability and interaction of the target species with the fishery/gear, such as inter-and intra-specific interactions (Skerritt et al, 2020), bait attraction (McQuinn et al, 1988), temperature (Lizárraga-Cubedo et al, 2015;Mullowney, 2016;Bakke et al, 2019), soak time (Bennett, 1974), and fisher targeting behaviours and associated local ecological knowledge (Santos et al, 2019). Factors that create variability in commercial LPUE are often overlooked because of over-simplistic approaches and static-environment assumptions, which are frequently built into traditional assessment and management tools (Szuwalski and Hollowed, 2016).…”

“…Accurate geolocations would help improve the integration of fisheries-dependent LPUE into assessments of data-poor fisheries (Skerrit et al, 2020). In the EU, vessel monitoring systems (VMS) have been useful for monitoring, control, and surveillance purposes as well as producing evidence for some ecological indicators (EC, 2008).…”

“…In the UK, pot fisheries have historically had a lower profile than well-documented fin-fisheries, although many have undergone significant expansions in effort and landings. The main C. pagurus and H. gammarus fisheries in the UK are considered to be either fully exploited or overexploited (Mesquita et al, 2017;CEFAS, 2020a, b), although due to the open access nature of these fisheries and lack of total allowable catch limits, regulatory responses to overfishing currently hinges primarily on access/effort limitations and implementation of technical measures (Skerrit et al, 2020). Furthermore, mandatory reporting systems for the majority of inshore vessels <12 m targeting these fisheries have been at low spatial resolution and relied on paper submissions which are prone to (unintentional) inaccuracies.…”