New PhD on squid recreational fishing
12/12/2014 11:41Miguel Cabanellas Reboredo
squid fishery
2014
The social relevance of recreational fisheries and their impact on the exploited resources and on the ecosystems have been widely recognized. However, the impact of recreations fishing is still rarely accounted for when assessing the population dynamics of targeted species.
The European squid Loligo vulgaris is a paradigmatic case-study. In the Balearic Islands (NW Mediterranean), this species is targeted by both the commercial and the recreational fishing sectors. The commercial squid fishery is relatively well known but the effect of the recreational sector on the population dynamics of L. vulgaris is currently unknown although potentially relevant. The assessment and management of recreational fisheries is particularly challenging due to the difficulties in estimating both, catches and fishing effort. Accordingly, the main objective of this Ph.D. Thesis is to estimate the recreational squid harvest. To face this challenge requires a socio-ecological approach, by which the ecological characteristics of the squid, the social characteristics of the angler and the interactions between them have been tackled.
The first section of the Ph.D. Thesis provides new insights linking some features of the squid life-history with the recreational fishing effort patterns. First, it is demonstrated that during the cold season (winter-spring) squid expand their spawning area to inshore waters, probably searching for the environmental conditions that maximize spawning success (e.g., sea temperature). This pattern is in accordance with the hypothesis that squid undergoes inshore spawning migrations. Accordingly, recreational fishers (anglers) exploit squid when they approach to the coast for spawning. Second, squid moves more actively at nighttime than during the day. This pattern was revealed using acoustic tracking telemetry and it is in accordance with the hypothesis of “feeding at night and spawning during the day". Accordingly, anglers exploit squid at sunset (using line jigging), when squid has already shift to the feeding state and lures are still visible Once solved the life-history patterns of L. vulgaris, the next step involved the understanding of the fishery dynamics. All boats fishing squid were recorded (on-boat censuses) in order to disentangle the drivers of angler's site (and day) choices. Both, catch-related (expected harvest) and non-catch related variables (e.g., sea condition and distance to the nearest homeport) play a relevant role. This Ph.D. Thesis provides fine-scale (1 km2 day-1) estimates of the recreational fishing effort.
Harvest not only depends on effort but on catch. To assess the effect of the environment on squid catchability, a set of experimental fishing sessions were performed. The combination of variables such as low windspeed, low atmospheric pressure and days close to the new moon maximized catch rates, although the main variable involved in catch fluctuations was sea temperature. Catches are higher during the cold season, which is again in accordance with the hypothesis that squid undergoes inshore spawning migrations. Moreover, the 30 minutes period around sunset is the more efficient than any other 30 minutes period before or after sunset for capturing squid. This second pattern is again in accordance with the “feeding at night and spawning during the day" hypothesis.
During the above-mentioned experimental shing sessions, a potential indirect effect of jigging was detected: some squid escape by losing one or both tentacles. The possible indirect effect of tentacle loss was tested through tank experiments. The results showed that loosing tentacles significantly decreased the predation effciency, which in turn may affect long-term survival and fitness. We suggest that such a (possible) ghost fishing should be considered.
Finally, this Ph.D. Thesis proposes a new framework for estimating harvest byb integrating the above-mentioned information. This framework combines model-based estimates of effort (varying in space and time) with model-based estimates of catches per unit effort (varying in time and on the angler type). In order to account for the angler heterogeneity, anglers were classified into three types according with the answers to a short interview. The questionnaire was designed for revealing angler's skill and experience. By including heterogeneity of anglers, the estimated harvest gained in precision. The recreational squid harvest in Palma Bay was estimated in 20.5 tonnes during 2010. This means that recreational harvest represents 34% of the total squid landings by the entire commercial eet of Mallorca Island during the same year (59.5 tonnes). Although to explicitly model the population dynamics of squid is outside the scope of this Ph.D. Thesis, this is the first empirical data quantifying the importance of the recreational fishing of L. vulgaris. The knowledge provided certainly should constitute a baseline for a long-term monitoring program, and it demonstrates that stock assessment should incorporate the role of the recreational fishery.
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