Article

Using artificial devices for identifying spawning preferences of the European squid: Usefulness and limitations

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

Sustainable management of exploited stocks demands, among others issues, to identify the spawning spatio-temporal patterns and eventually to protect the spawning grounds of the target species. Squid seems to aggregate at this crucial period of the life-history, which implies increasing vulnerability to fishing. Unlike those of other loliginid species, the spawning preferences of the European squid are largely unknown because finding egg clutches of this species in the wild is challenging. Validated records from research programs are virtually inexistent but unsystematic records from, for example fisherman, suggest that squid spawns regularly on artificial structures. Here, we report for first time a description of the spatio-temporal pattern of squid spawning on artificial devices (ADs). Thirty ADs were deployed over one year at a marine reserve (Cabrera National Park). ADs were distributed covering the three main types of benthic habitat, and ranging from 5 to 50 m depth. ADs were sampled monthly. Three main patters have been evidenced: (i) squid would prefer sandy bottoms for spawning, (ii) spawning would peak in spring, and (iii) squid would expand their spawning areas to shallower waters during the coldest months. It is debatable to extrapolate these patterns to those actually takes place in natural conditions. However, given the heavy fishing effort exerted on squid and data scarcity, the precautionary approach supports to take data from ADs as a starting point for advising sustainable management. Assuming that spawning at ADs and at the wild are correlated, the first pattern may be related to the faster marine currents that prevail on sandy bottoms or the smaller abundance of potential predators in these habitats. The second pattern may be related with the typical phytoplankton–zooplankton cascade that, in the Western Mediterranean, takes place just preceding spring. While the third pattern is in accordance with the hypothesis that squid may undergo a spawning migration.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... temperature changes, strong currents, ripples), and biotic (e.g. predation) risks (Bloor et al., 2013;Cabanellas-Reboredo et al., 2014;Martins et al., 2018). Here, a second impact of artisanal coastal fisheries relates to the utilization of static fishing gears by these animals as artificial spawning substrates (Blanc and Daguzan, 1998;Melli et al., 2014;Grati et al., 2018). ...
... Squid attach their egg mops to rocks, debris and other hard objects on sandy to muddy bottoms (Jereb and Roper, 2010). Cabanellas-Reboredo et al. (2014) showed that L. vulgaris eggs were mostly recorded between depths of 18 and 50 m and on artificial spawning substrates located on sandy bottoms. Egg depositions were found less on rocky bottoms and only a few on phanerogam beds. ...
... This means squid egg mops need to be laid on physical or artificial substrates that are easily distinguishable by other females (Hanlon et al., 2002), which explains why hemp lines with floats were the most successful spawning substrate for squid in this study. Similar artificial spawning substrates based on ropes vertically positioned in the water column have been used both for the European squid (Cabanellas-Reboredo et al., 2014;Feyjoo et al., 2016) and for other Loligo sp. (e.g. ...
Article
Full-text available
We investigated the effect of trap-like gear deployment on the survival of European squid Loligo vulgaris and common cuttlefish Sepia officinalis eggs laid on various surfaces of these gears. In parallel, a detailed assessment of the two species’ egg deposition patterns on such gears was performed with respect to both the fishing season and their preferences for artificial spawning substrates. Hemp ropes with floats were the most preferred spawning substrate for squid, whereas cuttlefish mostly deposited their egg clusters on the plastic mesh of rectangular pots. Almost no egg laying was observed on traps where netting frame was coated with antifouling paints (copper oxide or zinc pyrithione). A high proportion of squid egg mops and cuttlefish egg clusters were shown to either be lost or to die after a period of continuous operation (i.e. hauling and retrieval at frequent intervals), which exceeded egg incubation periods. It is thus advised that coastal fishers either completely avoid operating static gears, which act as artificial spawning substrates on the spawning fields or use gears with materials that are repellent for these animals to approach and lay their eggs, such as nets coated with antifouling substances.
... The prolonged duration or increased rainfall intensity and continuous turbulent sea condition may prevent spawners from reaching their preferred spawning locations that are suitable for egg laying, development of eggs or survival of paralarvae, or a combination of all these. It has been reported that loliginids have a preferred spawning habitat (Cabanellas-Reboredo et al. 2014), having more favourable environmental conditions, which may enhance paralarval survival. Eventually, the variability and unexpected changes in the ecosystem could either weaken or strengthen the inherent biological advantages, and ultimately impact recruitment (Roberts 2005). ...
... A similar pattern has been documented in the temperate loliginid Loligo reynaudii, where a synchronization of egg laying and productivity occurs so that the hatchlings emerge at the peak of production, also coinciding with an increase in temperatures. Similarly, depending on the sea temperature, European squids are reported to move from deeper waters to inshore waters (Cabanellas-Reboredo et al. 2014). This may enable the hatchlings to grow, by taking advantage of the abundance of prey (Sauer et al. 1992;Roberts 2005). ...
Article
Indian squid, Uroteuthis (Photololigo) duvaucelii (Loliginidae) constitute an important component of the inshore cephalopod fisheries along the eastern Arabian Sea. Local environmental variation plays an important role in species–environment interactions in neritic squids, which inhabit nearshore/coastal waters. Such ‘active’ and ‘passive’ responses of squids to environmental changes is crucial in understanding their relationships and influence on the biological processes, distribution and abundance of the fast-growing short-lived coastal loliginids. The empirical relationship between squid abundance and the variability in rainfall and sea surface temperature (SST) were explored in a tropical monsoon fishery. Monthly catch rates (catch per fishing hour) of squids in commercial trawl during 1987–2009 were used as the abundance index. Linear regression models with ARIMA errors were fitted with catch per unit hour time series as dependent variable and rainfall and SST as exogenous variables. While rainfall was observed to have a negative effect on squid abundance, the SST recorded a positive impact. ARIMA models provided satisfactory fit to observed data and forecast of 22 months. Given that the squid life-cycle is a function of their environment, this result is relevant in forecasting squid biomass for the management of tropical monsoon fisheries.
... We applied this strategy to the recreational fishery for squid at Palma Bay (Mallorca Island, NW Mediterranean; Fig. 1) and used 2010 as the model year. A detailed description of this recreational fishery is provided by Cabanellas-Reboredo et al. (2014b). ...
... vulgaris and L. forbesi) pooled into a single commercial category, whereas anglers only exploit L. vulgaris. In addition, we focused here on the most important type of recreational fishing effort (line jigging during sunset), but a small number of anglers target squid by trolling at night, by line jigging at sunrise (Cabanellas-Reboredo et al., 2011, 2012b, 2014b or by fishing from shore. Regardless, it seems indisputable that recreational fishing appears to play a relevant role in the population dynamics of squid. ...
Article
Although some stocks are being severely exploited by recreational fishing, estimating the biomass extracted (harvest, H) by recreational fisheries is difficult, especially for marine recreational fisheries. One way to estimate H by recreational fisheries is to combine the fishing effort (E) with catch-per-unit-of-effort (CPUE) data. However, naively ignoring heterogeneity in E and CPUE may result in biased and imprecise estimates of H. We propose a framework to address three relevant heterogeneity levels: the spatial and temporal heterogeneity of recreational E, environmental effects on recreational CPUE, and the variability in angler skills (between-angler heterogeneity). Specifically, we combine (i) space-time model predictions of E (number of boats per km2) on the day scale (i.e., fishing trips), (ii) environmentally driven model predictions of daily catch (number of squid per fishing trip), and (iii) off- and on-site surveys to account for angler heterogeneity. The precision of the H estimates was assessed using bootstrap confidence intervals. This framework was applied to the recreational fishery for the squid Loligo vulgaris at Palma Bay (Mallorca Island, western Mediterranean). The estimated effort was 15,750 angler-fishing trips (95% CI: 13,086 to 18,569), which yielded an annual harvest of 20.6 tons (95% CI: 16.9–24.5). This harvest was estimated to represent 34% of the total commercial landings in Mallorca, which highlights the importance of recreational harvesting and the need to account for recreational fisheries to improve squid stock management. The framework proposed here provides a promising tool for estimating H in other heterogeneous recreational fisheries and may be the first step toward assessing the actual impact of recreational fisheries on squid populations.
... Based on the Pearson correlation test (Table 3), the water temperature, salinity, dissolved oxygen (DO) and pH levels did not correlate with the presence of squid eggs. This corresponds with the research of Cabanellas-Reboredo et al (2014), who found that sea surface temperature (SST) did not significantly affects squid spawning preferences. However, interaction between SST and depth has suggested a significant effect on adult squid, prompting them to spawn more in these areas. ...
... According to Squires et al (2013) temperature affects egg size where smaller eggs are produced at higher temperatures and the rate of egg laying where eggs are laid faster at higher temperatures. In addition, Cabanellas-Reboredo et al (2014) reported that the presence of squid has a strong relationship with depth and habitat variables where squid tend be attracted to deeper artificial devices and to artificial devices located on sandy bottoms. This study showed that fish eggs were virtually absent in the attractor. ...
Article
Full-text available
The objective of this study was to assess the ability of artificial aggregating substrates for fish and squid eggs attachment. This study was performed in an area adjacent to Bidong Island on the East Coast of Peninsular Malaysia. The aggregating devices were set up at three different water depths (6 m, 12 m and 18 m) in nine locations. The presence of fish eggs and squid eggs in attractors were collected every two weeks. Scuba diving was used to collect data in different water depths. This study revealed that no fish eggs were recorded on the attractors, but there was a presence of squid eggs in seven locations. In addition, the results also showed that environmental factors such as temperature, salinity, pH and dissolved oxygen (DO) not significantly affect the presence of squid eggs. However, the location and depth of the attractors from the water surface have a significant effect on squid egg attachment in atractor.
... Based on the Pearson correlation test (Table 3), the water temperature, salinity, dissolved oxygen (DO) and pH levels did not correlate with the presence of squid eggs. This corresponds with the research of Cabanellas-Reboredo et al (2014), who found that sea surface temperature (SST) did not significantly affects squid spawning preferences. However, interaction between SST and depth has suggested a significant effect on adult squid, prompting them to spawn more in these areas. ...
... According to Squires et al (2013) temperature affects egg size where smaller eggs are produced at higher temperatures and the rate of egg laying where eggs are laid faster at higher temperatures. In addition, Cabanellas-Reboredo et al (2014) reported that the presence of squid has a strong relationship with depth and habitat variables where squid tend be attracted to deeper artificial devices and to artificial devices located on sandy bottoms. This study showed that fish eggs were virtually absent in the attractor. ...
Conference Paper
Full-text available
Fish Aggregating Devices (FADs) serve as habitat manipulation for fishes and can be used for determination of fishing ground for fishermen. Various hypotheses explained why floating artificial habitats are successful in attracting fishes. The existence of fish around floating objects (FADs) could be related to the habit of spawning on the aggregators of FADs. The objective of this study is to determine if coconut fronds attractors are used as substrates for fish eggs. The surveys were conducted at 9 locations of FADs between Latitude 050 35’N and Longitude 1030 00’E in coastal waters of Terengganu, on the east coast of Malaysian Peninsula. Samplings were conducted every 2 weeks on 4 strands of coconut fronds at different depths of water for identification of fish eggs. Underwater camera was also used to support the observation. The preliminary results of the study showed that attractors on FADs could be the substrates for fish eggs. There was significant correlation between the depths of attractors and the presence of fish eggs on the FADs (P<0.05).
... All these substrates are also important breeding grounds for cephalopods, fish, snails, etc. (e.g. Cabanellas-Reboredo et al., 2014), also observed in this study). ...
Article
Full-text available
Sessile benthic communities are an important element of marine ecosystems, yet their temporal patterns remain poorly understood. For this reason, the temporal changes of the fouling community on brick plates in Piran Bay, Gulf of Trieste (northern Adriatic Sea), were studied for two calendar years. The aim of this study was to identify the settlement of dominant native and alien species on artificial substrates and their temporal occurrence, both in terms of season and duration of submersion. In addition, we tried to assess the impact of the placement period on developing communities. The dominant taxonomic groups were bryozoans, which accounted for almost half of the total coverage (46%), serpulid polychaetes (25%) and bivalves (11%). Most of the species belonging to the dominant taxa occurred throughout the year, with the peak of occurrence in summer. The first settlers included serpulids and bivalves, which were constantly found on the plates together with bryozoans. Alien and cryptogenic species represented about 13% of all taxa found during the study. This highlights the importance of bare artificial structures erected outside typical hotspots for alien species; they serve as a springboard for the spread of alien fouling species. The communities that formed on plates placed in different seasons showed significant differences between them. High bryozoan coverage characterized the communities placed in winter and spring, while the plates placed in summer and autumn were dominated by serpulid polychaetes. These differences are the result of species seasonality as well as the interaction between them. The study demonstrates the importance of timing for initial colonization. It can be linked to the placement of the bare substrate for the development of the community, and provides a baseline for research and projects involving underwater constructions and the detection of alien species.
... However, some areas of the shallow reef and deep habitat that appeared to be suitable for egg-laying consistently supported few cuttlefish throughout the season. Densities in the deep habitats tended to peak slightly later in the season than the shallow habitats, which suggests cuttlefish reproductive activity may wane as the season progresses, and individuals shelter more often among the tall algal stands of the deep habitat; or possibly indicates an overflow effect as available egg-laying sites in the shallow habitat are exhausted (Cabanellas-Reboredo et al., 2014). ...
Article
The giant Australian cuttlefish, Sepia apama, forms a dense spawning aggregation at a single known location across its wide southern Australian distribution. After a rapid increase in fishing pressure on the aggregation in the late 1990s, a series of fishing closures were introduced before any biological information could be collected. We surveyed the habitats, timing, and spatial distribution of the spawning aggregation over 4 years, using underwater visual transects and passive tagging, to assess the suitability of the closures. We found that the annual aggregation was both temporally (April-August) and spatially (over 8 km of coastline) localized and predictable, with a consistent peak in abundances in late May-early June. Cuttlefish densities were generally highest over the shallow, broken bedrock habitat, which was more extensive in several sites left open to fishing. Although the original closure covered about 43% of the hard substrate, it accounted for only 23-37% of the total cuttlefish abundance. The extremely high densities recorded during this study verified that this is a massive spawning aggregation for cuttlefish species worldwide, and that it could be highly vulnerable to overexploitation in the absence of adequate protection, because it is so spatiotemporally predictable and localized. © International Council for the Exploration of the Sea 2017. All rights reserved.
... In the Mediterranean Sea, they are subject to intense fishing activity and constitute an important fraction of the commercial landings of trawlers, artisanal fisheries (handline jigging with attraction lights and seine fishing; Guerra and Rocha 1994;Lefkaditou et al. 1998;Cabanellas-Reboredo et al. 2011) and recreational fisheries (Cabanellas-Reboredo et al. 2014). ...
Article
Full-text available
Eye lens of 196 Loligo vulgaris and 205 Loligo forbesii collected by trawl surveys from 2013 to 2015 in Sardinian waters (Mediterranean Sea) were analysed for age determination. In an alternative to the technique previously used in Sepia officinalis and Enteroctopus megalocyatus, in this study, we proposed the elimination of decalcification and dehydration steps to reduce the time of lens processing. In addition, lenses were included in epoxy resin, which was then subject to lapping, to ensure clear reading and counting of the increments. The number of increments counted in L. vulgaris (59–520) and in L. forbesii (51–543) was strongly related to mantle length and weight of the animals, with no statistical differences between the sexes. Assuming daily growth increments, L. vulgaris was estimated to have a life span of 17 months for males and 14 months for females, while L. forbesii males had an estimated life span of 18 and 16.5 months for females. The exponential model was the best fit for growth data for both species and sexes, showing higher growth for males in comparison with females. These results preliminarily indicate that the eye lens is a valid tool for age determination of the two Loliginidae species, but it would benefit from validation by additional studies.
... Fishing for squid and cuttlefish is carried out in the Galician rías (Guerra & Castro, 1988;Simón, Rocha & Guerra, 1996) when these cephalopods arrive to reproduce (Cabanellas-Reboredo, Alos, Palmer, March & O'Dor, 2012;Cabanellas-Reboredo et al., 2014;Castro & Guerra, 1990). The Ría of Vigo (Figure 1) was selected as a study area because the biology of both squid and cuttlefish has been well studied (Castro & Guerra, 1990;Guerra & Castro, 1988;Otero et al., 2015). ...
Article
A new methodology based in the use of fishers’ knowledge and cost-effective tools to obtain information about marine recreational fisheries (MRF) is presented. The squid and cuttlefish fishery of the Ría of Vigo (NW Spain) was selected because it is managed in a data-poor environment. In-depth interviews (57) were conducted with fishers, collecting ecological and socio-economic information. A cartography of fishing grounds based on their knowledge was obtained, while the intensity of effort and catches was mapped by the monitoring of two vessels with low-cost GPS data loggers. The 102 shore anglers and 248 recreational boats catch 8 t/year of European squid Loligo vulgaris and 11 t/year of common cuttlefish Sepia officinalis (11% of total catches on these species in the area). Shore anglers fish from 11 ports, while boat fishers use 14 fishing grounds (covering 30 km2). Most of the catches (86%) are landed by boats, and their CPUE is higher in the outer part of the Ría of Vigo. The use of fishers’ knowledge and cost-effective monitoring is encouraged to obtain information for the management of MRF. Given the economic contribution of MRF (260,000 €/year in direct expenses), this activity should be considered in the regulations.
... Thirty devices (cephalopod egg capsule aggregators; CECA; Figure 1) were randomly deployed between June 2012 and June 2013 throughout Cabrera National Park (Mallorca; northwest Mediterranean). The CECAs were recovered monthly, and the attached egg masses were collected (see Cabanellas-Reboredo et al. 2014 for sampling details). Three egg capsules from each egg mass were randomly collected. ...
Article
Full-text available
The embryonic development of the squid Loligo vulgaris was observed from 183 egg 30 masses collected from special devices deployed throughout Cabrera National Park 31 (Baleares Islands, Western Mediterranean Sea). The sequence alignment analysis of 32 gene cytochrome oxidase I revealed that all embryos belonged to L. vulgaris. In total, 33 549 egg capsules were examined. Viable egg capsules (420) were classified into one of 34 five maturation stages according to the primary external features. The length of the 35 viable egg capsules varied between 40 and 170 mm, and increased with embryonic 36 development. The non-viable capsules (129) were categorized into 4 groups: I (Ginger root), 37 non-viable II and III, and empty egg capsule (IV). The percentage of non-viable capsules was 38 92.25. Empty capsules accounted for 7.75% of the total non-viable egg capsules. Embryonic 39 development was classified into a second scale of eight stages. Egg capsule stage and 40 embryonic stage were significantly related (n=420; p<0.001), facilitating the 41 determination of the embryo developmental phase based on the outward appearance of 42 the egg capsules. The embryo development stage based on the external features of the 43 egg capsules might constitute an innovative tool for in situ embryological data collection. 44 This new method is neither time consuming nor invasive, and could be helpful in fishing 45 cruises for scuba diving visual census in natural habitats and laboratory culture. The 46 slight variability in the developmental embryonic stages within the egg capsule from the 47 same egg mass was identified. The origin of this asynchrony is discussed. The 48 chronological appearance of organs was similar to that of the six loliginid species 49 previously examined. However, some developmental changes in the timing or rate of 50 events (heterochronies) were observed: Hoyle’s organ was formed earlier in L. vulgaris 51 and the appearance of ventral chromatophores was slightly delayed (2 days) compared 52 with the other species considered.
... They mainly feed on fish, with little frequency variation but different species composition depending on the region (Roper et al. 1984, Collins et al. 1994, Coelho et al. 1997, Wangvoralak et al. 2011. Seasonal and daily spatial migrations, related to reproduction and feeding, are known to occur in both species (Rocha & Guerra 1999, Cabanellas-Reboredo et al. 2012, 2014b. However, to date nothing is known about the diet of L. vulgaris and L. forbesii in the Mediterranean, although different aspects of their life cycle (e.g. ...
Article
The squid Loligo vulgaris (LV) and L. forbesii (LF) are 2 cephalopod species occurring in the Atlantic Ocean and the Mediterranean Sea. Bathymetric segregation allows the co-existence of both species, with LV preferentially inhabiting the shallow shelf and LF living on the shelf-break and upper slope grounds. In this paper, the feeding habits of LV and LF were studied for the first time in the Mediterranean, by means of stomach content analysis (1452 and 900 individuals of LV and LF, respectively). The main objective was to determine the diet of both species, analysing temporal and ontogenetic diet changes and inferring predator-prey interactions. Fish were by far the most important prey in both squid, followed by crustaceans and cephalopods. Prey composition revealed the bathymetric segregation of both species in the Mediterranean. Whereas LV preferentially consumed typical coastal species of sparids and gobiids, LF preyed on slope inhabitants such as myctophids and euphausiids. Ontogenetic shifts of diet occurred in both squid, but took place at contrasting sizes, suggesting that the factors triggering them might be speciesspecific. The diet of small-sized LV individuals was more dependent on bottom-living organisms than in large individuals, which preyed mainly on benthopelagic fish. During the main reproductive period in spring, LV increased the consumption of highly nutritive prey such as polychaetes (nereidids). Size-related differences in LF diet during the second half of the year indicated a deeper distribution of large individuals, preferentially preying on mesopelagic species and being thus involved in benthic-pelagic coupling.
Article
To improve limited knowledge of the predation behaviour of the loliginid species, this study is the first to examine the hunting and feeding behaviour of Loligo vulgaris. Hunting and feeding strategy, as well as body patterning of the squid were described in laboratory experiments during which, two prey types, characterised by different size and mobility (prawn and fish), were offered to the squid. According to the type and distance of the prey, three hunting strategies were observed: to seize larger, farthest and high-mobility prey (fish), squid used tentacles as the main predatory tool (tentacular lunge attack); squid conducted an arm-opening attack to capture smaller and less mobile prey (prawn), but a mixed-strategy using both arms and tentacles was executed when the prawn was further away. Once captured, prawns were consumed alive, while the squid administered a lethal bite to the fish prior to consumption. Fish were always eaten in head-caudal fin direction. Size-feeding strategy differences were also observed. Largest squid ate faster and consumed the entire prey, while smaller squid rejected certain parts of the fish prey. Better prey-handling skills and larger feeding apparatus (e.g., beak) of larger squid (older/experienced individuals) are the likely causes. Finally, a prey-specific body pattern was performed depending on the prey exigency levels.
Article
The common dentex Dentex dentex is an iconic endangered species in the Mediterranean, where it is a target species that is sought after for small-scale, recreational and spearfishing fisheries. The reproductive biology of D. dentex in the natural environment is poorly known; therefore, the reproductive strategy of the species was assessed through a combination of reproductive traits and growth characteristics (estimated from length-at-age data), the size/age of sexual maturity and the energetic dynamics. A total of 358 wild fish, ranging in total length (L-T) from 19 to 84.7 cm, was sampled at Mallorca Island (Western Mediterranean) from March 1996 to June 1999. The sex ratio was skewed towards females (1.361); however, the length composition was not different between sexes (p = 0.551). Three young immature individuals (< 28 cm L-T, 0.8% individuals) were rudimentary hermaphrodites, offering support for classification as a late gonochoristic species. The age composition, determined based on the sagittal otolith, ranged from 0 to 26 years (yr). The von Bertalanffy growth function did not differ between sexes (F = 2.58, p = 0.762): L-infinity = 76.581 cm, K = 0.127 yr(-1), t(0) = -2.335 in a combined function. The maturity ogives for size and age showed that females achieved 50% maturity at 34.922 cm L-T and 3.3 yr, and males, at 33.812 cm L-T and 2.5 yrs. The onset of annual ripening took place in December, whereas vitellogenesis occurred from February to April. The spawning peak was in April and May for both males and females. A generalised linear model (GLM) showed that female size did not significantly affect the spawning season, whilst the seasonal component affected both the onset and end of spawning (GLM, p < 0.005). The gonadosomatic index (I-G), hepatosomatic index (I-H) and relative condition index (K-R) varied significantly with the reproductive season for females, and IG varied for males. The microscopic observation of the gonads showed that fecundity is likely determinate, with an asynchronous oocyte development before spawning and a clear ovarian bimodal organization after the onset of spawning. The oocyte density variance of 85% was explained by the oocyte diameter, which also offered support for the trait of determinate fecundity. Female weight explained 84% of the observed variance for fecundity. Liver storage seemed to be the primary source of energy for maturity, which suggests a combination of capital and income breeding. The results suggested a reproductive strategy of type A, with balanced trade-offs between survival, growth and reproduction. At present, no management measures are being directed to D. dentex; herein, we suggest a minimum landing size of 35 cm L-T to ensure a higher proportion of larger fish to preserve the stock.
Conference Paper
Full-text available
Resumen La pesca recreativa ha sido muy poco estudiada en Galicia a pesar de la importante influencia que ejerce sobre los ecosistemas marinos y sobre sus recursos. La pesca de cefalópodos resulta particularmente desconocida pese a que es practicada por un importante número de pescadores en Galicia. Con el fin de obtener información de esta actividad, se seleccionó la Ría de Vigo como área de estudio y se realizaron encuestas a pescadores del área. En las encuestas se recogió información ecológica, social y económica de la pesquería y se evaluó el uso del conocimiento tradicional de los pescadores (CET) para mapear sus caladeros. Además, se monitorizó la actividad de dos embarcaciones mediante dispositivos acumuladores GPS y el registro de sus capturas, para mapear la distribución de la intensidad del esfuerzo y de las capturas. Los cefalópodos más importantes en el área fueron el calamar común Loligo vulgaris (Lamarck, 1798) y a la sepia común Sepia officinalis (Linnaeus, 1758). Se estimó que en la Ría de Vigo operan 231 pescadores desde tierra, 156 embarcaciones destinadas a capturar sepia y 176 dirigidas a la captura de calamar. Los pescadores desde tierra identificaron 11 zonas de pesca situadas principalmente en instalaciones portuarias y los pescadores desde embarcación identificaron 22 caladeros de pesca de calamar y sepia, que ocuparon una superficie de 30 km 2. En general, el esfuerzo pesquero se ejerció mayoritariamente en la costa noroeste de la ría, zona que fue además la más productiva en términos de capturas. Las capturas anuales realizadas por estos pescadores (18 t) suponen un elevado porcentaje de las capturas comerciales sobre estas especies obtenidas en el área (45 t), por lo que es imprescindible incluir las capturas recreativas en los futuros modelos de gestión pesquera. Por otro lado, debe prestarse un adecuado reconocimiento a la importante contribución del sector recreativo a la economía local como resultado de los gastos que afrontan en embarcaciones y equipos de pesca.
Article
Full-text available
Some 290 species of squids comprise the order Teuthida that belongs to the molluscan Class Cephalopoda. Of these, about 30–40 squid species have substantial commercial importance around the world. Squid fisheries make a rather small contribution to world landings from capture fisheries relative to that of fish, but the proportion has increased steadily over the last decade, with some signs of recent leveling off. The present overview describes all substantial squid fisheries around the globe. The main ecological and biological features of exploited stocks, and key aspects of fisheries management are presented for each commercial species of squid worldwide. The history and fishing methods used in squid fisheries are also described. Special attention has been paid to interactions between squid fisheries and marine ecosystems including the effects of fishing gear, the role of squid in ecosystem change induced by overfishing on groundfish, and ecosystem-based fishery management.
Article
Full-text available
Temperature tolerance of common squid (Loligo vulgaris Lamarck, 1798) eggs in controlled conditions was investigated between May 21, 2002 and March 04, 2003. The treatments were performed as 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, and 28°C at 37 ppt. Illumination was kept at dim light for 13-49 days before hatching. A mean dorsal mantle length of hatchlings was measured as 2.74 mm ± 0.1 SD. In the trials, the eggs developed and hatched normally after 44-49 d at 12°C, 32-39 d at 14°C, 23-30 d at 16°C, 23-29 d at 18°C, 18-25 d at 20°C, 14-20 d at 22°C, and 13-19 d at 24°C, except at 6, 8, 10, 26, and 28°C. In the experiments, hatching rates and hatching success of the eggs ranged from 15.4 to 99.6% and from 9.3 to 98.5%, respectively, and significant differences were found between the treatments (χ2, p<0.05).
Article
Full-text available
Extensive studies of biology and life cycle, and the application of some stock-assessment techniques to South African chokka squid (Loligo vulgaris reynaudii) have contributed toward formulating management approaches for the species. Efforts to clarify the systematics preceded the biological, behavioral, population dynamics, lifecycle, and ecological studies. Management measures have progressed from simple ones designed to order the fishery and control effort, to a more structured approach that uses a closed season as the main management tool. Recent modeling studies have indicated that the stocks are nevertheless under pressure, at a time when there is a political imperative to allow new entrants into the fishery. There is consequently a need to introduce new methods of management (while maintaining effort control as opposed to catch control), which may ultimately lead to the introduction of an operational management procedure.
Article
Full-text available
Bathymetric distribution and aspects of the life history of the loliginid squid Loligo aulgaris (Mollusca: Cephalopoda) in the Catalan sea (NVy Mediterranean) Distribución batimétrica y aspectos del ciclo biológico del calamar Loligo uulgari.s (Mollusca: cephalopoda) en el ABSTRACT Of the 263 trawl catches studied during 1991 carried out at depth between 12 m and 645 m in the Catalan sea, Loligo vulgaris appeared in 68, at depth between 17 and 1g0 m. Negative allometric arowth was observed between mantle length and weight in both sexes. According with the seasonal bathymetric distribution of sizes, large animals (150-250 mm ML), maturing or mature were found in waters of less than 100 m depht throughout the year, but above all in autumn and winter; immature specimens (<150 mm ML) were present at all depths throughout the year. Two migratory movements were detected: small squid hatched near the coast displacing towards deep water, and large (maturing or mature) animals moving towards coastal waters to spawning RESUMEN De 263 pescas de arrastre realizadas durante 1991 entre 12y 645 m de profundidad en el mar Catalán, Loligo vulgaris fue capturado en 68 de los lances entre 17 y'1g0 m de profundidad. Se observó un crecimiento alométrico negativo entre el peso total y la lon-gitud del manto en ambos sexos. Se detectó una distribución batimétrica estacional. Ejemplares grandes (150-250 mm LM), madurando o maduros, se encontraron a menos de 100 m de profundidad durante todo el año, pero sobre todo en otoño e invierno; los ejemplares pequeños (<150 mm LM) aparecieron en todas las profundidades durante todo el año. Se observaron dos desplazamientos: los calamares pequeños que nacen cerca de la costa se desplazan hacia mayor profundidad y los grandes se mueven hacia la costa para la puesta.
Article
Full-text available
Published and anecdotal information was used to formulate a conceptual (logic) model which describes the biological components and dynamics of chokka squid spawning aggregations. Into this was integrated potential environmental influences. To determine quantitatively the impact of environmental factors on the spawning process (and ultimately catches), a theoretical methodology was developed based on the use of underwater video images to estimate the rate at which egg pods were deposited. Results from a pilot study undertaken off the Tsitsikamma coast of South Africa demonstrated the viability of this quantitative technique, and while not intended to be a definitive experiment, showed that: (i) an upwelling event was coincident with the formation of a spawning aggregation, supporting the hypothesis that changes in temperature trigger spawning; (ii) biological activities such as egg deposition, predator-induced interruptions in egg deposition, and absence of squid from the egg bed, occupied 19, 22, and 59% of the event time respectively, and (iii) spawning was completed in about 33 h in the absence of female immigration. An overall decline in the deposition rate, combined with the absence of adverse environmental conditions, indicated that spawning was terminated by the ovaries of female squid becoming partially or fully spent, rather than by environmental stimuli. Based on this experience, hardware was then designed and manufactured to realize the methodology, and it is currently being used in a new series of squid spawning experiments.
Article
Full-text available
Opportunistically collected information on sea temperature and wind was used in a preliminary investigation of physical factors affecting jigged catches of chokka squid Loligo vulgaris reynaudii. Results revealed sea temperature and wind to be correlated with catches during part of the summer upwelling season (October and December) in 1988. Multiple linear regression analysis confirmed that sea temperature was a highly significant explanatory variable (p = 0,0000) for catches from three boats, as well as for the overall catch. Wind direction also played a significant role (p = 0,0085) in the overall catch. A statistical linear multiple regression model is proposed for each boat and for the total catch. Upwelling events are suggested to play a major role in the availability of squid on the inshore spawning grounds ( Document Type: Research Article DOI: http://dx.doi.org/10.2989/025776191784287466 Publication date: December 1, 1991 More about this publication? 2003 - current volumes available in full-text. Click here. $(document).ready(function() { var shortdescription = $(".originaldescription").text().replace(/\\&/g, '&').replace(/\\, '<').replace(/\\>/g, '>').replace(/\\t/g, ' ').replace(/\\n/g, ''); if (shortdescription.length > 350){ shortdescription = "" + shortdescription.substring(0,250) + "... more"; } $(".descriptionitem").prepend(shortdescription); $(".shortdescription a").click(function() { $(".shortdescription").hide(); $(".originaldescription").slideDown(); return false; }); }); Related content In this: publication By this: publisher By this author: Sauer, W. H. H. ; Goschen, W. S. ; Koorts, A. S. GA_googleFillSlot("Horizontal_banner_bottom");
Article
Full-text available
A critical feature of effective marine reserves is to be large enough to encompass home ranges of target species, thereby allowing a significant portion of the population to persist without the threat of exploitation. In this study, patterns of movement and home range for Lethrinus harak and Lethrinus obsoletus were quantified using an array of 33 acoustic receivers that covered approximately three quarters of Piti Marine Reserve in the Pacific island of Guam. This array was designed to ensure extensive overlap of receiver ranges throughout the study area. Eighteen individuals (12 L. harak and 6 L. obsoletus) were surgically implanted with ultrasonic transmitters and passively tracked for 4 months. Both species displayed high site fidelity and had relatively small home ranges. The home ranges of L. harak expanded with increasing body size. Feeding of fish by humans, which was common but restricted to a small area within the study site, had little effect on the distribution of the resident populations. L. harak made nightly spawning migrations within the reserve between full moon and last quarter moon of each lunar cycle, coinciding with a strong ebbing tide. Results indicate that even small reserves can include many individual home ranges of these emperorfishes and can protect spawning sites for L. harak. These species are heavily targeted in Guam, and there are major demographic differences between fished and protected sites. This study shows the potential for protected areas to sustain reproductive viability in exploited populations.
Article
Full-text available
Annual landings of chokka squid (Loligo reynaudii), an important fishing resource for South Africa, fluctuate greatly, and are believed to be related to recruitment success. The ‘Westward Transport Hypothesis’ (WTH) attributes recruitment strength to variability in transport of newly hatched paralarvae from spawning grounds to the ‘cold ridge’ nursery region some 100–200 km to the west, where oceanographic conditions sustain high productivity. We used an individual-based model (IBM) coupled with a 3-D hydrodynamic model (ROMS) to test the WTH and assessed four factors that might influence successful transport – Release Area, Month, Specific Gravity (body density) and Diel Vertical Migration (DVM) – in numerical experiments that estimated successful transport of squid paralarvae to the cold ridge. A multifactor ANOVA was used to identify the primary determinants of transport success in the various experimental simulations. Among these, release area was found to be the most important, implying that adult spawning behaviour (i.e., birth site fidelity) may be more important than paralarval behaviour in determining paralarval transport variability. However, specific gravity and DVM were found to play a role by retaining paralarvae on the shelf and optimizing early transport, respectively. Upwelling events seem to facilitate transport by moving paralarvae higher in the water column and thus exposing them to faster surface currents.
Article
Full-text available
The small-scale common octopus (Octopus vulgaris) fishery in Galician waters (NW Spain) was studied using a model based on information obtained from fishers. The Gómez-Muñoz model was applied using information obtained from the artisanal Galician fleet from 1998 to 2000. This information was used to estimate catches per unit of effort (CPUE) and total catch for the whole directed creel fishery. A total of 73 interviews were conducted in 22 ports in the west part of ICES division VIIIc and 75 interviews in 16 ports in the north part of ICES division IXa. The estimated total catch during the fishing season for the whole Galician fleet was 5214 t (2528 t in VIIIc and 2686 t in IXa), and the average CPUE for the VIIIc and IXa fishing grounds obtained from the model was 44.11 and 23.83 kg haul-1 respectively. To test the reliability of the model, the outputs obtained for a subset of 35 ports (19 in VIIIc and 16 in IXa), were compared with the official statistics of these ports. The average official catch from 1997 to 2000 and estimated total catch data were significantly correlated.
Article
Full-text available
The importance of the south-west coast of Portugal as a spawning ground for the long-finned squid, Loligo vulgaris, was investigated between May 1993 and May 1994 at a site 3 Km East of Sagres. Hydrographic (temperature and salinity) observations were registered in situ and water samples were collected for laboratory determinations of chlorophyll a. Zooplankton was sampled with a 500 μm plankton net during 10mn trawls. Hydrographic and biological information was related to the occurrence of L. vulgaris egg masses at the site. The values of water temperature ranged from 13.0° C in January to 19.2° C in July, and the salinity varied between 35.3‰ in May of 1993 and 38.0‰, in November, December and March. The highest values for phytoplankton biomass were recorded in September and May, whereas the maximum Zooplankton abundance was recorded between July and September. The most important Zooplankton groups included cladocerans, copepods, crustacean larvae, fish eggs and appendicularians. We have concluded that the highest values for Zooplankton abundance were recorded when the greater number of egg masses of L. vulgaris were observed.
Article
Full-text available
In the present study the fish communities of the rocky bottoms of Cabrera Archipelago (Balearic Islands) are analysed and provide data for future evaluation of any changes produced by management. Visual counts were carried out by diving along transects situated in areas of rocky blocks at depths of -10 m, -25m, and -41 m and at vertical cliffs -15 m deep. In the 10 stations studied, 48 species belonging to 19 families have been recorded. The increase in depth principally produced a specific impoverishment and a decrease in the density of mesophagous and macrophagous carnivore species. This tendency bacame more noticeable changing from the infralittoral to the circalittoral stage. In the infralittoral stage the substrate rugosity was a more important factor than depth in the structure of the fish community. However, other specific characteristics of each zone such as algal cover, hydrodynamic conditions and fishing pressure, as well as habitat changes with size of some species, also affected the specific composition and demographic structure of the fish cummunity.
Article
Full-text available
In the Western Mediterranean, the European squid Loligo vulgaris is exploited by both commercial and recreational fleets when it spawns in inshore waters. The inshore recreational fishery in the southern waters of Mallorca (Balearic Islands) concentrates within a narrow, well-delineated area and takes place during a very specific period of the day (sunset). Another closely related species, L. reynaudii, displays a daily activity cycle during the spawning season (feeding at night and spawning in the day). Using acoustic tracking telemetry, we tested the hypothesis that L. vulgaris could display a similar daily activity pattern. We conducted 2 tracking experiments during May to July 2010 and December 2010 to March 2011, in which a total of 26 squid were tagged. Our results suggested that L. vulgaris movements differ between day and night. The squid moved within a small area during the daytime but covered a larger area from sunset to sunrise. The probability of detecting squid was greatest between depths of 25 and 30 m. The abundance of egg clutches at this depth range was also greater than at the other sampled depths. The distribution of the recreational fishing effort using line jigging, both in time (at sunset) and in space (in the 20 to 35 m depth range), also supports the ‘feeding at night and spawning in the day’ hypothesis.
Article
Full-text available
Egg masses of the loliginid squid Loligo vulgaris Lamarck, 1798 are attached to hard substratum or branched sessile organisms on the sea bottom. Embryonic development lasts from a few weeks to a few months, depending on the environmental water temperature. Because embryonic statolith growth of L. vulgaris is very sensitive to temperature under laboratory conditions, we analyzed the possibilities of determining past events in the squid’s early life from analysis of the embryonic area of statoliths of wild squid populations. The relationship between egg-incubation temperature and daily growth of embryonic statoliths under laboratory conditions was determined by tetracycline markings at 10 incubation temperatures ranging from 12 to 24.7°C. In addition, the mean width of embryonic increments in statolith collections of wild L. vulgaris from the Eastern Atlantic (Saharan Bank and NW Iberian Peninsula) and the Mediterranean Sea (Central and Eastern) was calculated. The temperature inferred from the embryonic increment widths of the statoliths of wild squid indicates that embryonic development of L. vulgaris in the regions sampled is likely to occur at temperatures ranging from 12 to 17°C. Mediterranean squid have wider embryonic increments than Atlantic squid, reflecting the slightly higher water temperatures in the Mediterranean Sea during the development of the egg masses. Eggs of L. vulgaris spawned off the NW Iberian Peninsula were estimated, on average, to remain at sea for 47 d, 1 wk longer than Mediterranean eggs (nearly 1 mo longer when comparing minimum and maximum ranges). A longer incubation time for egg masses attached to the sea bottom increases mortality risks. Conversely, slow development at a lower temperature can improve yolk conversion, producing larger hatchlings, and increased hatching competence is expected from such squid. Therefore, a compromise between longer-versus-shorter incubation time and related characteristics does exist.
Book
Full-text available
Over the past two decades, cephalopod molluscs have attracted increased attention from marine biologists and fishery scientists. Several species are important for European fisheries, as targets of small‐scale coastal fisheries and/or as bycatch in multispecies fisheries for demersal fish. The present report draws on a series of reviews prepared in 2005 for the CEPHSTOCK project (see Section 1). The taxonomy of the main resource species is reviewed (Section 2), and brief descriptions of each species are provided, along with information from studies of population genetics, habitat requirements of paralarvae and adults, and health and ecotoxicology (Section 3). The main fisheries are described, including illustration of gears used in specialized small‐scale fisheries and a discussion of the socio‐economic importance of the fisheries. The current status of cephalopod aquaculture is reviewed, highlighting notable advances in commercial culture of octopus and cuttlefish (Section 4). Current fishery data collection and fishery management are described, noting that there is no setting of landings quotas and no routine assessment of stock status. Options for stock assessment are discussed, drawing on one‐off assessments made during specific projects and current practice elsewhere in the world. The “live fast, die young” life history strategies of cephalopods present particular challenges, but parallels can be drawn with short‐lived fish (Section 5). Finally, the report looks to the future, reviewing possible effects of climate change on cephalopods. It discusses the future development of aquaculture and fisheries for cephalopods, including prospects for fishery forecasting and fishery management – especially in relation to the small‐scale directed fisheries. Various knowledge gaps are identified, and ideas for research to fill these gaps are presented.
Article
Full-text available
Cephalopods are highly sensitive to environmental conditions and changes at a range of spatial and temporal scales. Relationships documented between cephalopod stock dynamics and environmen-tal conditions are of two main types: those concerning the geographic distribution of abundance, for which the mechanism is often unknown, and those relating to biological processes such as egg survival, growth, recruitment and migration, where mechanisms are sometimes known and in a very few cases demon-strated by experimental evidence. Cephalopods seem to respond to environmental variation both 'actively' (e.g. migrating to areas with more favoured environ-mental conditions for feeding or spawning) and 'passively' (growth and survival vary according to conditions experienced, passive migration with pre-vailing currents). Environmental effects on early life stages can affect life history characteristics (growth and maturation rates) as well as distribution and
Article
Full-text available
Part of the spawning area of the squid, Loligo vulgaris reynaudii, was investigated over a 5-week period using a combination of hydroacoustic techniques, SCUBA dive transects and observations. Egg mass concentrations were identified by a Furuno FCY-663 echosounder, and these were positively confirmed by SCUBA diving. It was found that egg strands were concentrated into distinct, clumped spawning beds which were non-randomly distributed in the study area. Bottom substrata favored by spawning squid appeared to be sandy areas or low profile rocky reefs. The average number of eggs per strand was 148 (±37). This study examines different techniques to estimate numbers of squid eggs in the wild, which may have wider application. Two statistical techniques were used in an exploratory data analysis to estimate the total number of eggs present in the study area, using both random and non-random transect methods. A non-random technique of estimation on clearly defined egg bed areas was found to be the most appropriate, although egg number estimates to date are considered preliminary.
Article
Full-text available
It is believed that annual variability in chokka squid catches may be linked to recruitment success. For the oceanic Illex species, recruitment variability has been shown to be strongly related to changes in Western Boundary Currents (WBCs) as these play a major role in the life cycle. This paper investigates the role of currents in the early life cycle of chokka squid. A synthesis of currents on the Agulhas Bank is undertaken within the context of paralarvae food distribution and availability. Flow patterns are shown to be less defined and more complex than WBCs. Copepods are widely available for the paralarvae on the shelf, which suggests that starvation is not a limiting factor in chokka squid recruitment success. Instead of playing a positive role in the early life history of the chokka squid, currents appear to present a threat to the survival of paralarvae by removal from the shelf ecosystem. This can influence recruitment.
Article
Full-text available
The biological characteristics of the squid Loligo vulgaris from north France, northwest Portugal, the Saharan Bank, and the Greek Seas were analyzed to describe largescale biological patterns and to evaluate geographical variation in the Atlantic and the Mediterranean. In northwest Portugal and on the Saharan Bank population length structures are more complex due to extended spawning and recruitment periods. Squid spawn only between November and April in north France and the Greek Seas. Gonadosomatic indices decreased with decreasing latitude in the Atlantic, while the highest indices were found in the Mediterranean. Full maturity occurred at smaller size in northwest Portugal than in other areas of the Atlantic, and at similar size to Mediterranean squid. Length-weight relationship slopes increased from the north to the south in the Atlantic and in the Mediterranean. Multivariate analysis of seasonal biological indices demonstrated significant biological differences between squid of different areas, mainly in terms of size at maturity, male GSI and average body size and weight. Biological variability between areas was considered related to plasticity of responses to large-scale geographic environmental conditions.
Article
Full-text available
The Magnuson-Stevens Fishery Conservation and Management Act recognizes that fish stocks depend on healthy ecosystems and requires that fishery managers expand their management regimes to include the very basis of healthy fisheries—the habitat itself. The 1996 amendments to this primary United States marine fishery-management law include a new mandate to identify habitats essential to managed living marine resources and to take steps to ensure that those habitats remain healthy and can support sustainable fisheries. Until now, the legislative mandate for protecting habitat for marine and anadromous stocks came through statutes not specifically focused on the needs of commercial and recreational fish species. Now, there is explicit linkage between fishery-management programs, traditionally designed to manage the harvesting activity itself, and efforts to ensure that fishing and nonfishing activities do not undermine the productivity of the stocks. This emphasis on habitat health and productivity brings a broader ecosystem perspective to traditional fishery management. The insertion of essential fish habitat (EFH) provisions into fisheries management has been an enormous undertaking. The agency and the regional fishery management councils, working with other partners, completed the first stage of the process within very tight statutory deadlines. The councils have made use of all of the tools provided them under the act and the EFH regulations, such as designating habitat areas of particular concern (EFH-HAPCs), recommending fishing restrictions within special areas, defining priority research and information needs, and documenting threats and conservation measures appropriate for federal actions that may adversely affect EFH. This effort has entailed a great deal of scientific as well as policy analysis. We are currently implementing the federal consultation process to address threats to fish habitat in a consistent and timely manner. This new habitat thrust will align fishery managers and scientists with new allies in the habitat arena, increasing benefits to marine resource-management programs and fishery management. As suggested by the theme of this issue, an understanding and consideration of marine reserves and other special-area management concepts can benefit federal fishery management. This article gives an overview of how the fishery-management councils are fulfilling the essential fish habitat mandate by using a broader ecosystem approach to conservation that considers the ecological role of managed species, analyzes species' habitat needs from state waters to the high seas, and examines shifts in population health and sustainability over the course of decades.
Article
Full-text available
This paper presents data on the population structure, maturation patterns, fecundity, reproduction, and length–weight relationships of the European squid, Loligo vulgaris, in the Central Adriatic Sea. This species is one of the most valuable commercial cephalopods in the fishery of the Adriatic Sea, yet the population structure and reproductive biology are poorly known. The data are based on the analysis of 1583 individuals caught between 1998 and 2000 along the Croatian coast. In the major part of the year the sex ratio was close to 1:1, but in certain months males outnumbered females. Males were dominant in the smallest and the largest individuals, but at medium lengths females dominated. The length–weight relationship and dorsal mantle length at first sexual maturity for both sexes is given. Male and female reproductive outputs were counted and measured. Oocytes from the ovaries and oviducts of mature females were at various phases of development. Monthly changes of maturity indices, coefficients and frequency of appearance of advanced maturity stages showed a pattern of seasonal development with low values during summer and very high values during winter and spring. The spawning peaks were between January and May, but mature individuals were caught in all months, indicating that in the Central Adriatic Sea this species spawns throughout the year.
Article
Full-text available
Squid jigging experiments were carried out to determine whether differences occurred between different colors and lunar brightness in Middle Eastern coast of Aegean Sea. Five different colors of jigs (red, blue, green, orange and white) were used together in same angle. According to one-way analysis of variance results, red jigs were found to be the most efficient in squid capturing (p < 0.01). General linear model results proved that lunar brightness of full moon phase showed positive effects to squid catching (p < 0.01). The differences between jigs were statistically significant except between blue and green. In addition, the relationship between dorsal mantle length of captured specimens and color of jigs were not significant.
Article
Full-text available
IMPORTANT NOTE: Do not be alarmed by the image resolution on this proof! Due to the limitations of our laser printer, figures can appear different than they will actually be on the printed journal. This laser proof is for checking design, accuracy of all type, and general scheme. Also be aware any photos are printed at a much coarser screen (resolution) and may show some loss of detail. ABSTRACT An interfaced marine information system is developed for integrated analysis of fish-eries of five commercially important cephalopod species in Greek waters of the Eastern Mediterranean. The system combines data on the spatial and temporal patterns of cepha-lopod population dynamics focusing on geo-distribution of abundance, environmental variation, fisheries, spawning areas and migration habits. The system is developed as a customisation of a workstation ARC/INFO environment and features a series of innova-tive GIS map-overlay and integration routines for analysis and modelling of surveyed, statistical, and remote-sensed data. Geo-referenced datasets include cephalopod catch and landings, coastline-bathymetry, bottom substrate types, and a set of environmental variables provided by satellite sensors (AVHRR/sea surface temperature and SeaWiFS/ chlorophyll-a concentration) and climatologic datasets (sea surface salinity). The inno-vative aspect of this marine system is the integration of species life history data to GIS analysis. Species preferences on certain spawning conditions, migration habits, and depth ranges are used as constraints in GIS analysis and integration. The application of GIS and Remote Sensing technologies has proved useful for the mapping of seasonal spatial com-ponents of cephalopod population dynamics. Results from this application may be used for information-based species management proposals, which is the goal of further devel-opment of this marine information system.
Article
Squid, cuttlefish and octopuses, which form the marine mollusc group the cephalopods, are of great and increasing interest to marine biologists, physiologists, ecologists, environmental biologists and fisheries scientists. Cephalopods: ecology and fisheries is a thorough review of this most important animal group. The first introductory section of the book provides coverage of cephalopod form and function, origin and evolution, Nautilus, and biodiversity and zoogeography. The following section covers life cycles, growth, physiological ecology, reproductive strategies and early life histories. There follows a section on ecology, which provides details of slope and shelf species, oceanic and deep sea species, population ecology, trophic ecology and cephalopods as prey. The final section of the book deals with fisheries and ecological interactions, with chapters on fishing methods and scientific sampling, fisheries resources, fisheries oceanography and assessment and management methods. This scientifically comprehensive and beautifully illustrated book is essential reading for marine biologists, zoologists, ecologists and fisheries managers. All libraries in universities and research establishments where biological sciences and fisheries are studied and taught should have multiple copies of this landmark publication on their shelves.
Article
We used fishery population models to assess the potential for marine fishery reserves, areas permanently closed to fishing, to enhance long-term fishery yields. Our models included detailed life history data. They also included the key assumptions that adults did not cross reserve boundaries and that larvae mixed thoroughly across the boundary but were retained sufficiently to produce a stock-recruitment relationship for the management area. We analyzed the results of these models to determine how reserve size, fishing mortality, and life history traits, particularly population growth potential, affected the fisheries benefits from reserves. We predict that reserves will enhance catches from any overfished population that meets our assumptions, particularly heavily overfished populations with low population growth potential. We further predict that reserves can enhance catches when they make up 40% or more of fisheries management areas, significantly higher proportions than are typical of existing reserve systems. Finally, we predict that reserves in systems that meet our assumptions will reduce annual catch variation in surrounding fishing grounds. The fisheries benefits and optimal design of marine reserves in any situation depended on the life history of the species of interest as well as its rate of fishing mortality. However, the generality of our results across a range of species suggest that marine reserves are a viable fisheries management alternative.
Article
The selection of spawning habitat of a population of Octopus vulgaris that is subject to a small-scale exploitation was studied in the Cíes Islands within the National Park of the Atlantic Islands of Galicia (NW Spain). The technique used was visual censuses by scuba diving. We conducted 93 visual censuses from April 2012 to April 2014. The total swept area was 123.69 ha. Habitat features (season, depth, zone, bottom temperature, swept area, bottom substrate type, and creels fishing impact) were evaluated as predictors of the presence/absence of spawning dens using GAM models. O. vulgaris has a noteworthy preference for spawning in areas with hard bottom substrate and moderate depth (approximately 20 m). The higher density of spawning dens (1.08 ha−1) was found in a surveyed area of 50.14 ha located in the northeastern part of the northern Cíes Island. We propose to protect the area comprised from Punta Escodelo to Punta Ferreiro between 5 and 30 m depth. This area has a surface of 158 ha equivalent to 5.98% of the total marine area of the Cíes islands. The strengths and weaknesses of a management strategy based on the protection of the species’ spawning habitat are discussed.
Article
The selection of spawning habitat of a population of Octopus vulgaris that is subject to a small scale exploitation was studied in the Cíes Islands within the National Park of the Atlantic Islands of Galicia (NW Spain). The technique used was visual censuses by scuba diving. We conducted 93 visual censuses from April 2012 to April 2014. The total swept area was 123.69 ha. Habitat features (season, depth, zone, bottom temperature, swept area, bottom substrate type, and creels fishing impact) were evaluated as predictors of the presence/absence of spawning dens using GAM models. O. vulgaris has a noteworthy preference for spawning in areas with hard bottom substrate and moderate depth (approximately 20 meters). The higher density of spawning dens (1.08/ha) was found in a surveyed area of 50.14 ha located in the northeastern part of the northern Cíes Island. We propose to protect the area comprised from Punta Escodelo to Punta Ferreiro between 5 and 30 m depth. This area has a surface of 158 ha equivalent to 5.98 % of the total marine area of the Cíes islands. The strengths and weaknesses of a management strategy based on the protection of the species’ spawning habitat are discussed.
Article
Recreational fishing effort greatly fluctuates in space and time. Therefore, one of the most relevant conceptual issues when managing recreational fishing is to understand the primary complexities associated with anglers' preferences in selecting site and day, and the way that these choices affect the catch. However, two practical pitfalls (data acquisition and statistical issues) are hampering progress towards the understanding of this problem. In this study, we propose several strategic improvements and apply them to the recreational squid fishery in Palma Bay (Balearic Islands). The spatial scenario (20 km width) was surveyed 63 times (visual censuses) during two years. For each of the 173 grid cells (1 km2) into which Palma Bay was divided, the fishing effort (number of recreational boats targeting squid) was recorded. In addition, a number of variables intended to summarize any potential driver of anglers' choices were also recorded. The principal drivers of squid recreational fishing in Palma Bay appeared to be expected harvest and distance to the nearest port, but the effect of these variables was clearly modulated by sea conditions. The fine-scale estimates of effort (daily predictions for each 1 km2 cell) provided here represent the first step towards understanding angler preferences, estimating total catches, and selecting the best management options for avoiding conflicts between stakeholders, thus ensuring resource sustainability.
Article
Experimental fishing sessions simulating the operating procedures of the recreational fishery for the European squid that operates at inshore Palma Bay (Balearic Islands, Spain) were conducted to investigate the effects of environmental variables on squid catches. The catch per unit of effort (cpue) of recreational-like jigging sessions showed a seasonal pattern (higher cpue during colder months). Two alternative hypotheses can explain such a pattern. First, squid could migrate inshore during colder months to seek spatio-temporal windows within which the sea temperature maximize spawning success. Second, the timing of the seasonal reproductive peak and the growth rate of any given cohort would result in a higher percentage of squid whose body size is greater than the gear-specific vulnerability threshold during the colder months. The combination of environmental variables that maximized cpue was a low sea surface temperature, a low windspeed, low atmospheric pressure, and days close to the new moon. A specific period of the day, narrowly around sunset, favoured the catches. Within this narrow period, the sunlight is still sufficient to allow the recreational fishing lures to be effective, and the squid have already shifted to a more active pattern of movement characteristic of the night-time period.
Article
The spatial distribution of Pinna nobilis densities have been analysed through a geostatistical approach in the MPA of Cabrera National Park, Balearic Islands (Spain), Western Mediterranean Sea. Regression kriging was used to model the effect of environmental variables on the density of living individuals of P. nobilis and generate a predictive map of its distribution within the MPA. The environmental variables considered for the model were: depth; slope; habitat type and heterogeneity; wave exposure; and MPA zoning. A total of 378 transects were randomly distributed with a total of 149,000 m2 surveyed at a depth range from 4.2 to 46 m. The recorded P. nobilis densities are among the highest in the Mediterranean Sea. With respect to the prediction model, results indicate that benthic habitats play a key role in the spatial distribution of P. nobilis, with higher densities in seagrass meadows of Posidonia oceanica. The fan mussel population density peaked at 9 m depth, decreasing with depth. Also, decreasing densities are expected with increasing exposure to waves. The predicted map shows some hotspots of density different in size and distributed along the MPA, and provides valuable information for the spatial conservation management of this species.
Article
Anthropogenic impacts from urbanization, deforestation, and agriculture have degraded the riparian margins of waterways worldwide. In New Zealand, such impacts have caused changes in native vegetation, enhanced invasion by exotic grasses, and altered river bank morphology. One consequence has been a great reduction in obligate spawning habitat of a diadromous fish, Galaxias maculatus. Juvenile G. maculatus comprise a culturally important fishery that has been considerably reduced over recent decades. Rehabilitation of riparian vegetation needed for spawning is relatively straightforward, but slow. We hypothesized that artificial spawning habitats could accelerate restoration of fish egg production by creating an environment that would support at least the same density and survival of eggs as non-impacted vegetation. We tested three artificial devices (straw bales, straw tubes, and moss tubes) in degraded and intact sites. Eggs were laid in all of these with numbers and survival usually exceeding that in riparian grasses. Where habitat was degraded, artificial spawning habitats yielded up to 10,000 eggs compared to none in nearby natural spawning habitat. The ground-level environment of artificial habitat was similar to that of intact vegetation in buffering ambient temperature and humidity fluctuations. Crucial properties of the artificial habitats were (1) shelter to provide shade and hold moisture; (2) accessibility to allow adult fish to deposit and fertilize eggs; and (3) robustness to provide reliable surfaces and protection for the eggs during their development. We show that artificial spawning habitats are a viable short-term alternative to rehabilitating spawning habitat while legacy effects abate and riparian vegetation recovers.
Article
Fluctuations in the number and size of spawning perch (Perca fluviatilis) in Lake Geneva were evaluated and compared each year from 1984 to 2011 in two locations. This evaluation was based on: (1) each mature female lays only one egg strand per year and (2) the number and size of mature females are well correlated with those of their egg strands. Egg strands were counted and measured at two locations in France and in Switzerland. The collection of egg strands from either artificial substrates (France) or by direct sampling of the natural lake bottom by a diver (Switzerland) did not seem to affect the results. In most years the number and mean width of egg strands fluctuated in the same way in both locations. In addition, yearly perch catches were correlated with the number of egg strands at both locations. However, more small egg strands were found in France than in Switzerland, whereas the reverse was true of large egg strands. Fishing pressure concentrated to a greater extent on small perch in France than in Switzerland could explain this difference.
Article
The South African squid fishery is based on a single species, Loligo reynaudi, locally referred to as chokka and commonly found around the Agulhas Bank and West Coast shelf of South Africa. The existing long term rights for participation in the fishery expire at the end of 2013 and a new set of rights will have to be issued. Progress made to date in achieving the objectives of the South African Marine Living Resources Act of 1998 (MLRA), including progress towards greater equity, will be an important consideration in allocation decisions. The draft Small-Scale Fisheries Policy, scheduled to be adopted in 2013, could also influence the criteria to be used. This study updates the information on the current structure and functioning of the squid jig sector and considers the likely performance of two alternative access allocation scenarios against the current and evolving policy goals. The study reaffirms that the squid fishery is an important contributor to human well-being in South Africa and particularly in the Eastern Cape Province but there is scope for improvement in the extent of transformation and equity. The study concludes that, as a result of a common lack of experience and capital amongst potential new entrants, the risks associated with transformation in this fishery are likely to be high, especially if the option of allocating rights to community-based legal entities was to be used. The risks could be reduced by ensuring that a number of pre-conditions were met. These include, amongst others, not allowing total effort in the fishery to increase; ensuring effective management by the responsible government authorities; adequate capacity building of new entrants, whether individuals or cooperatives; and ensuring new entrants have viable business plans.
Article
Squid are short-lived ecological opportunists which generally have a lifespan of about 1 year. Their populations are labile and recruitment variability is driven, to a greater or lesser extent, by the environment. This variability provides a challenge to management because fisheries for short-lived species are best managed by effort limitation and it is difficult to set effort on a rational basis in the absence of information about the abundance of the next generation prior to recruitment. However, recent research has shown that recruitment variability in several squid species can be partly explained by environmental variability derived from synoptic oceanographic data. In the eastern Pacific coastal upwelling system a fishery for Dosidicus gigas has grown rapidly during the last decade and abundance and catch rates seem to be linked to the El Niño/southern oscillation (ENSO) cycle. ENSO is one of the best understood ocean/climate systems and so with increased knowledge of the life cycle biology of D. gigas, this fishery may provide a good model for understanding environmentally driven recruitment variability in exploited squid populations.
Article
From March to September, cuttlefish lay eggs on natural substrata (tubes of polychaetes, Zostera leaves, algae) and also on artificial surfaces (cuttletraps, ropes, branches). In Morbihan Bay, during this period, between 18 and 40 million eggs are laid on cuttletraps. From March to May, fishermen empty traps every two days. They stack the traps on a pontoon-bridge before further use, and so a great quantity of eggs are destroyed. The objective of this study is provide artificial substrata (similar to natural surface) to compensate for significant loss of eggs. The artificial surfaces, in the form of floating ropes, are well adapted to the hydrodynamics of Morbihan Bay. The characteristics of the ropes best suited for egg laying are a diameter about 8mm and a length between 30 and 90cm with a preference for 50cm. The number of eggs per surface is estimated at 2200, and the surfaces should be easy to manipulate by fishermen.
Article
Management for sustainable fisheries requires effective tactics for limiting exploitation rates. Limitation based on annual stock assessments and total allowable catches calculated from these assessments can be very dangerous, and marine protected areas (MPAs) are one means by which to limit exploitation rate directly even when total stock size is highly uncertain. This application of MPAs would probably require much larger areas than are now envisioned for limited objectives related to protection of seed spawning stock and local biodiversity. It might in fact cause a basic shift in thinking—from regarding MPAs as exceptional areas to regarding fishing areas as the exception (as is now the practice in, e.g., salmon and herring fisheries). The present paper describes the use of ECOSPACE, a new modeling tool based on ecosystem simulations, for preliminary determination of how large MPAs need to be; ECOSPACE models suggest that dispersal, trophic responses (prey depletion, increased dispersal of predators in response to competition), and spatial fishing-effort responses (concentration of fishing near MPA boundaries) are all likely to reduce the effectiveness of small MPAs. The models suggest we should see not simple high-low density differences across MPA boundaries but rather spatial gradients from low density in exploited areas to high density near the centers of larger MPAs. Such spatial density gradients should be accompanied by spatially organized 'trophic cascade' patterns if trophic interactions are important determinants of abundance. MPA design can work with or against spatial variation in fishing effort caused by economic cost and risk factors; ECOSPACE can help to demonstrate ecological consequences of alternative design strategies, but the most important uncertainties are about socioeconomic responses (cooperation or competition) rather than ecological ones. Design of experimental policies and monitoring programs for evaluation of MPAs should proceed from careful modeling to define likely spatial, temporal, and trophic scales for both ecological and fishing responses.
Article
I. Der vorliegende Beitrag, dessen Problemstellung viele Einzelfragen umfasst, gilt der Erforschung der Biologie von Loligo vulgaris Lam. Die Arbeit fusst auf der Untersuchung von etwa 12000 in der Nähe von Den Helder erbeuteten Stücken. Die Art kommt in dieser Umgebung vom April bis August allgemein und in den übrigen Monaten vereinzelt vor; sie pflanzt sich hier regelmässig fort. 2. Das Wachstum wurde mittels der Analyse von Frequenzkurven der ventralen Mantellängen festgestellt. 3. Anfang Mai haben die Längenfrequenzkurven der fast ein Jahr alten â™`â™` einen Gipfel bei 13-14. cm und die der fast zwei Jahre alten bei 2 1 cm, während drei Jahre alte Tiere wahrscheinlich selten vorkommen. Eine schematische Wachstumskurve der â™`â™`gibt Abb. 4. 4. Die â™â™wachsen, bis sie eine Länge von etwa 12 cm erreicht haben (d.h. bis sie 1/2-3/4 Jahre alt sind) gleich schnell wie die â™`â™`. Im zweiten Lebensjahre wachsen sie erheblich langsamer als die â™`â™`, so dass die Gipfel ihrer Frequenzkurven im Monat Mai bei etwa 13-14 cm und etwa 17 cm liegen. Langsames Wachstum im zweiten Lebensjahre ist gleichfalls bei den â™â™ von Loligo pealii Les. und Sepia officinalis L. festgestellt worden. Dreijährige â™â™von L. vulgaris scheinen selten vorzukommen. 5. Die einjährigen Tiere erscheinen durchschnittlich später im Frühling als die zweijährigen. Gleiches finden wir bei vielen zum Fortpflanzungsgebiet ziehenden Fischen und Vögeln. 6. Das Geschlechtverhältnis der Laichzügler ist ungleich; im Gesamtergebnis wurden 57% â™`â™` erbeutet. Durchschnittlich ist der Prozentsatz der â™`â™` anfangs etwas höher als später im Sommer, was aber nicht für jedes einzelne Jahr zutrifft. Die Reihenfolge der Geschlechter auf dem Zuge zum Fortpflanzungsgebiet wird vergleichend besprochen und es werden die Zusammenhänge mit der Paarungsbiologie behandelt. 7. Das Laichen dauert solange die Tiere das Gebiet in grosser Menge besuchen, also vom April bis August. In der 2. Maihälfte, wenn die meisten Tiere anwesend sind, erreicht es seinen Gipfelpunkt. 8. Bei den im selben Jahre geborenen â™`â™`enthält der Hoden schon im Oktober Spermatozoen. Seine Entwicklung geht im Laufe des Winters weiter, erreicht Mai-Juli den Gipfelpunkt um im August wieder abzunehmen. Wie weit sie im zweiten Winter wieder zurückgeht, konnte nicht festgestellt werden. Von den zwei Jahre alten Tieren. lässt sich nur sagen, dass der Hoden im Frühling und Vorsommer stark entwickelt ist und dass er sich im August wieder rückbildet. 9. Die im selben Jahre geborenen â™`â™`haben schon im Dezember Spermatophoren im Spermatophorensack. Bis zu ihrem Erscheinen im April übertrifft bei ihnen (sowie bei den zweijährigen â™`â™`) die Spermathophorenproduktion den Verbrauch (der dann wohl gleich Null zu setzen ist). Sobald die Tiere eingetroffen sind, übertrifft aber der Verbrauch die Produktion, welche jedoch nicht aufhört. Das Ergebnis ist, dass die Spermatophorensäcke immer leerer werden. 10. Die im selben Jahre geborenen â™â™haben im Dezember keine Eier im Ovidukt, während die Eier im Ovar noch sehr klein sind. Akzessorische, Nidimental- und Oviduktdrüsen stehen noch im Anfang ihrer Entwicklung. Zwischen Dezember und April entwickelt sich das Ovar stark; eine Abnahme zu Ende des Sommers konnte nicht festgestellt werden. 11. Vor der Ankunft der Tiere im Laichgebiet häufen sich Eier an im Ovidukt, während noch keine abgelegt werden. Die Ovidukte sind also mehr oder weniger gefüllt. Kurze Zeit nach dei Ankunft werden mehr Eier abgelegt als solche an den Ovidukt abgegeben werden, und die Zahl der Tiere mit leeren oder wenig gefüllten Ovidukten nimmt zu. Nach Ende Mai aber halten Verbrauch und Ersatz im Durchschnitt gleichen Schritt. Wahrscheinlich werden die Eier nicht kontinuierlich, sondern in einigen Gelegen abgesetzt. 12.
Article
Age, growth and maturation of Loligo vulgaris were studied by examination of growth increments within statoliths of 294 specimens (mantle length, ML, ranging from 31 to 498 mm) caught on the west Saharan shelf between 1985 and 1988. Maximum age was 335 d (290 mm ML) for females, and 396 d (498 mm ML) for males. Growth rates varied considerably among individuals with a greater range in males. Sexual dimorphism in length was apparent after about 210 d. Males and females diverged considerably in weight, with males reaching a greater weight after about 180 d. Growth in length between 124 and 396 d was best described by a power function, while growth in weight was best described by the Gompertz function. Males started maturing at 180–210 d and mature males ranged in age between 250 and 396 d; while females started maturing at 240–270 d and mature females ranged between 285 and 335 d. Loligo vulgaris hatched throughout the year with two distinct peaks; in winter (December - early March) and summer (June-July). The life cycle of L. vulgaris populations on the west Saharan shelf lasts ~1 y, with large males (>450 mm ML) living slightly longer.
Article
Loligo vulgaris is the most abundant and commercially important species of squid in Portuguese waters. The species presents a complex population structure due to a short life-cycle, highly variable growth rates and a long spawning period. The latter characteristics combined with the marked seasonality of the Portuguese coast results in individuals that are born in different seasons being influenced by different environmental conditions, notably water temperature, as has previously been shown.In the present study, we have taken animals belonging to each of two temperature-based hatching cohorts (cold and warm cohorts – CC and WC) and determined the fecundity and egg size of individuals on either one, in order to determine whether animals in different cohorts followed different reproductive strategies.Significant differences were found between the cohorts regarding reproductive investment, fecundity and size of oocytes. Individuals of the CC (larger and older when reaching maturity) had lower fecundity than individuals of the WC, but presented larger oocytes. WC females (smaller and younger at maturity) present higher fecundities and higher GSIs. Such differences further demonstrate the high plasticity and adaptability of these organisms to environmental conditions and highlight the advantage of integrating environmental variables in fisheries assessment.
Article
A biological characterisation of the populations of Loligo forbesi and Loligo vulgaris from the Portuguese coast is attempted by analysing morphometric and reproductive data, obtained from 1817 specimens of L. forbesi and 3940 of L. vulgaris, during 1990–1992.Based on the proportions of each of five maturity stages, and the proportion of mated females in monthly samples between January 1990 and June 1992, as well as analyses of the fluctuations of calculated gonadosomatic indices (GSI) and maturation indices (MI), spawning was found to take place (in autumn and winter for L. forbesi) throughout the year (for L. vulgaris), but with peaks of breeding in autumn and winter.Two different size groups at maturity were found in both species, one reaching full maturity at 180 mm dorsal mantle length and the other closer to the maximum size reached by each species and sex.No clear seasonal pattern in sex ratios was observed for either species.Characterisation of the relationship between length and weight in both sexes of both species is given.