How lure prevalence, survival rate and maturity status affect catchability in cuttlefish trap fishery
Introduction
Low impact and fuel-efficient fishing is gradually becoming more important (Suuronen et al., 2012). Static gears, such as pots and traps, are considered less severe than towed gears, possessing several appealing characteristics including low energy use, minimal habitat impact, and low bycatch (Jørgensen et al., 2017; Thomsen et al., 2010). Moreover, contrarily to static nets such as gill, trammel and tangle nets animals caught in traps are enclosed and not entangled allowing them to stay alive and unharmed until the gear is hauled (Miller, 1990; Uhlmann and Broadhurst, 2015; Vasconcelos et al., 2019). Besides ensuring product quality this also increases survival rates of incidental catches and discarded fauna (Vasconcelos et al., 2019). Traps can be deployed individually or in strings, have a variety of shapes and sizes and are widely used for harvesting diverse species, mainly crustaceans and cephalopods, namely the octopus and the cuttlefish.
In southern Europe, trap fishing is widely practiced for harvesting the common cuttlefish, Sepia officinalis L., constituting a sustainable métier (Tzanatos et al., 2013) with high socioeconomic significance in several areas of the Atlantic Ocean and Mediterranean Sea (Pereira et al., 2019; Vasconcelos et al., 2019). Similar to trammel-nets targeting this species, cuttlefish trap fisheries in Europe are seasonal, coinciding with its migration from deep to shallower waters thus becoming an exploitable resource for coastal fishers (Belcari et al., 2002). However, cuttlefish catches display a different seasonal pattern between these gears, with trammel nets exploiting stocks between winter and spring (Belcari et al., 2002; Lefkaditou et al., 2002; Tzanatos et al., 2005) and traps between late spring and summer (Pereira et al., 2019). This opposite pattern between gears was clearly evidenced in the comparative study of Belcari et al. (2002) and in the experimental study of Ganias et al. (2021) in Thermaikos Gulf (North Aegean Sea).
The cuttlefish is among the most important cephalopods in Hellenic marine fisheries landings (Lefkaditou et al., 2007, 2002; Pierce et al., 2010). Thermaikos Gulf and the Thracian Sea are the main fishing grounds for the cuttlefish in Greece (Lefkaditou et al., 2007, 2002), together with the remaining fishing areas of the N. Aegean Sea contributing to 75 % of the total cuttlefish catches in Hellenic Seas for the period 1996–2018 (NSSG 2018). In this area, the small-scale fishery (SSF) targeting cuttlefish is practiced exclusively with trammel nets with diagonal mesh of inner panel ranging from 64 to 80 mm (Lefkaditou et al., 2004). In contrast to fishing techniques implemented in the early 1990s to capture octopus, such as plastic pots (Lefkaditou et al., 2007), cuttlefish are not targeted by any trap-like gear in Greece. Even though, Ganias et al. (2021) suggested that cuttlefish traps could be used as a profitable and less impacting alternative to trammel nets in Greek SSF, displaying lower discards ratio, consuming less fuel and providing the opportunity to extend the fishing season, normally ending in May, by at least two months.
Although cuttlefish trap fishing possesses several appealing characteristics regarding its profitability and sustainability, there is a fundamental knowledge gap about the improvements required in the selectivity and environmental footprint of this static gear. Cuttlefish trapfishing can include either the use of artificial spawning substrates inside the traps for attracting females or the use of sexually mature females as lures for attracting males (Pereira et al., 2019; Pierce et al., 2010; Watanuki et al., 2000). However, still little is known on the behavioural interactions of cuttlefish with traps and whether they can be affected by the physical characteristics of the fishing-ground area. Other important factors including the shape and size of trap entrance and the optimum soaking time still need to be resolved. This study performed a series of experimental trap hauls to address these knowledge gaps and identify the optimum fishing protocol and trap entrance dimensions for this potentially new métier for Greek SSF.
Section snippets
Materials and methods
Fishing surveys were performed during January–June 2019 off Nea Michaniona fishing port, an important fishing ground for cuttlefish in Thermaikos Gulf. Field experiments were carried out with a chartered coastal fishing boat (8 m, 2.3 GT, 43 hp) deploying 20 identical netting traps of semi-rectangular shape (thereafter called cuttletraps after Blanc and Daguzan (1998)). Each cuttletrap comprised a metal frame covered by DyneemaTM netting with 22 mm stretched mesh (D-net) and had two openings
Results
A total of 67 longline operations were carried out involving 670 cuttletraps. From these traps, 268 (40 %) were baited with a lure, 100 (15 %) contained a shrub inside and the remaining 302 (45 %) were left empty. Concerning lure gender, 243 were females, 21 were males, while in 4 lures sex was undetermined. Lure ML ranged between 104 and 179 mm (mean 129.6 mm) and decreased with sampling month, following the seasonal decrease in cuttlefish size (Fig. 3).
Concerning lure condition, 42 % remained
Discussion
Cuttlefish trapfishing can include either the use of artificial spawning substrates inside the traps for attracting females or the use of sexually mature females as lures for attracting males (Pierce et al., 2010; Watanuki and Kawamura, 1999). The importance of lures in cuttlefish catches reported in this study, as opposed to the weak or zero-performance of empty traps or traps with shrubs, respectively, suggests that the effectiveness of these fishing methods can be affected by the
CRediT authorship contribution statement
Konstantinos Ganias: Supervision, Methodology, Data curation, Formal analysis, Visualization, Writing - original draft, Funding acquisition. Irini-Fotini Kompogianni: Methodology, Data curation. Georgios Christidis: Methodology, Data curation, Formal analysis.
Declaration of Competing Interest
The authors report no declarations of interest
Acknowledgments
The present work was performed within the framework of ECOSEPIA project (eco-sepia.bio.auth.gr/). The authors are grateful to E. Voultsiadou and C. Chintiroglou for fruitful discussions and to C. Antoniadou, X. Simeonidou, K. Georgiadis and A. Plepel for their help during samplings and work in the lab. Special thanks are due to the captain of the chartered vessel F. Karydas for sharing his knowledge and his insights during all stages of this work. Two anonymous reviewers are greatly thanked for
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