Tub gurnard, Chelidonichthys lucerna (Linnaeus, 1758), is a Mediterranean-Atlantic benthic species usually captured as by-catch by Portuguese traditional fisheries and considered the most important commercial fish species of the family Triglidae. However, to date, little is known about its habitat residency and whether the species can be considered a marine estuarine-dependent fish. Otolith microchemistry has proven effective in providing information about fish movement patterns throughout different water salinities. In this study, core-to-edge transects of Sr:Ca in the fish saccular otoliths of 35 juveniles of C. lucerna captured in March 2007 by a scientific survey along the Portuguese coast were used to assess the species movement between brackish and marine waters. Data suggest that most individuals (97%) have an estuarine-dependent profile, with 63% showing a clear presence in marine waters during the early life history periods. Evidence of an estuarine residence throughout the fish life cycle was found in only 3% of individuals. Ba:Ca profiles did not reflect an inverse relationship with Sr:Ca salinity results but corroborated findings from other authors about the influence of upwelling processes and freshwater runoffs on Ba incorporation into the otoliths of coastal fish. Furthermore, the data also showed that C. lucerna can occupy and migrate among habitats with diverse salinity degrees, showing high environmental plasticity and adaptation.

The purse seine fishery is one of the most important fisheries in Portugal, accounting for about 50% of landings in weight. Historically, the sardine (Sardina pilchardus) is the target species of the purse seine fleet. However, with the decline of the sardine stock and the reduction of annual quotas, this fleet has supplemented its yields by capturing other pelagic species such as chub-mackerel (Scomber colias), horse mackerel (Trachurus trachurus) and anchovy (Engraulis encrasicolus). This work aims to investigate changes in the purse seine fleet activity and catch and landings compositions associated with the decline of sardine, including inter-annual variations of fishing effort, catch, landings and slipping compositions, using on-board observations from 2006 to 2018. The Portuguese mainland coast was split in three main areas: North, Centre and South (from Viana do Castelo to Olhão, as describe in Feijó et al., 2018). During the study period (2006-2018), the observers were trained to follow the same standard protocol (Feijó et al., 2012) on-board commercial vessels (Length-overall >16 m). Most trips were carried out within the framework of PNAB/EU-DCF. Since 2010 and in the ports of Peniche, Olhão and Portimão, 80 trips were performed within the scope of SAFESEA and Life+MARPRO projects (Marçalo et al., 2015). Data were collected on fishing set characteristics (number, depth, geographic position), fishing activities (trip total duration and time spent in steaming, searching, fishing and resting as described in Feijó, 2013) and catch compositions (total biomass and species composition for retained, slipped and discarded catch). Each net deployment was counted as a fishing set. Between 2006-2018, more than 400 trips and 450 sets were recorded, corresponding to 0.5% of the total fleet effort (Silva et al., 2015). On-board observation work was carried out in more than half of the national fleet. Fishing occurred throughout the year but effort decreased between November and April due to voluntary area closures (in the North and Centre areas, fishing stops in February and March), sardine ban restrictions (2012-2018) and bad weather conditions. In earlier years, most trips were around 9h long with one to two sets observed. During the study period, there was an increase in the number of sets (3-4 sets) performed and time dedicated to searching in order to obtain the same catch and yields. Sardine catches and landings declined mostly due to quota restrictions, and were compensated by the increase of chub mackerel catches and landings. Changes in the target species were also observed although sardine was still the main species captured. In the 2017 and 2018, an increase in anchovy catches and landings was also observed. The reduction of annual quotas and establishment of daily limit quotas led to the increase of slipping, creating the differences between catches and landings. We observed behavior changes in the fleet along the country, such as a search for new fishing grounds and species with more market value. Our results are of interest to stakeholders as they provide a perception of changes in the fishery at the national and regional level.

In Portugal, the purse seine fishery is one of the most important fisheries, accounting for about 40% by weight of landings on the Portugal mainland. The fishery targets several small and medium pelagic species, being sardine (Sardina pilcharus) and chub mackerel (Scomber colias) the main landings. Sardine landings peaked in 2008, decreased 20% until 2011 and dropped sharply since 2012 to below the annual catch limit. Chub mackerel as the second most important species, their landings increased continuously from 2009, and the total landed in this fishery fluctuated until today. This work aims to study the Portuguese purse seine fleet activity and catch composition for 2009 to 2013 using data from daily landings and on board observations at the mainland fishing ports. The study area was divided into three areas, North (Caminha to Figueira da Foz), Centre (from Peniche to Sines) and South (Portimão to Olhão). Data on purse-seine fishing activities and catches were collected by observers onboard commercial vessels (length-overall>16m) operating along the Portuguese coast between 2009 and 2013. Most trips (108 in 179) were carried out within the framework of the European Commission Data Collection Regulation (Programa Nacional de Amostragem Biológica/EU-Data Collection Framework) and data were collected using a standard protocol (Feijó et al. 2012). Since 2010, additional data were obtained within SAFESEA and Life+MARPRO projects (http://marprolife.org/) in Peniche, Olhão and Portimão. During the study period, an average of 149 purse-seiners made around 12 000 trips per year (Silva et al., 2015).We observed 179 trips and 229 sets in Portuguese purse seine fleet, so the observation effort represents 1.49% of daily landings. The capture observed was around 21 tons (North= 7,8 tons, Centre = 5,7 tons, South = 7,1 tons), and landings were around 18,5 tons (North= 6,9 tons, Centre = 4,4 tons, South = 6,6 tons). Although, chub-mackerel was the dominant capture, but not all its capture was landed. Over the period, sardine captures and landings decreased until 2013. By area, sardine captures decreased during the period. In the centre have been observed more landings of sardine, specially in 2013. The decline of sardine landed in the centre and south ports has been compensated by increasing capture and landings chub mackerel. The discards by "slipping" were more frequent in the North, mainly because of the implementation of daily limit quotas. Slipping is the deliberate release of the catch when the skipper finds reasons not to transfer part or the total catch, such as daily quotas, minimum sizes or mixture with not commercial species) In the Southwest, “slipping” usually resulted from mixture with non-commercial species that would decrease the landing price. That’s the main reason that capture is different of purse-seine landings.