Sea Lice Control II

ABSTRACT

Sea lice, Lepeophtheirus salmonis, mobile stages were caught using a light trap, in cages holding Atlantic salmon, Salmo salar, and their abundance determined through calculation. Seasonal changes were shown with an increase in abundance as the temperature increased toward the end of the season. Analysis of manual lice-count data indicated variations in lice abundance between cages with and without deployed light traps. Analysis indicated that these variations were in larval presence (P = 0.006) and presence of gravid females (P = 0.015), but not in abundance of in pre-adults (P = 0.172). Cage net condition also affected the abundance and infection intensity of sea lice on Atlantic salmon within aquaculture cages. Abundance of larvae were affected by net condition (P = 0.01), as were abundance of pre-adults on salmon (P = 0.04). The infection intensity of gravid females, however, did not vary with net condition (P = 0.74). Other species of zooplankton such as, American lobster, Homarus americanus, larvae and various Brachi-pod larvae, were also collected with the light trap. The light trap, as presented in this research, could provide an alternate method of lice control in aquaculture cages.     

The influence of wind and temperature on the catch rate of the American lobster (Homarus americanus) during spring fisheries off eastern Canada

The effects of wind and temperature on catch rate of American lobster (Homarus americanus) in the Baie des Chaleurs and off Cape Breton Island in Eastern Canada were investigated. Data on lobster catch and the number of trap hauls were available through a fishermen's volunteer logbook program, bottom temperatures were measured from thermistors either moored nearby or placed inside lobster traps and wind measurements were obtained from local airports. In the Baie des Chaleurs and off the east coast of Cape Breton, a positive and significant correlation was found between the mean temperature change during the 24 h prior to the traps being hauled and the change in the average catch of lobsters per trap haul. Catch rates rose with increasing bottom temperatures and fell with declining bottom temperatures. Higher correlations between changes in temperature and catch rates occurred at sites where the temperature variance was greater. The short‐term fluctuations in lobster catch rates corresponding to temperature changes are hypothesized to result from behavioral changes affecting lobster activity. In both study areas, the large temperature variability was mainly forced by alongshore winds producing upwelling and downwelling, consistent with a classical Ekman response. The effect of the winds on lobster catch is shown to be principally due to their influence on ocean bottom temperatures. Along the south coast of Cape Breton, no relationship was found between catch rates and either temperature or wind, perhaps because lower lobster abundance resulted in a lower signal‐to‐noise ratio. The results of this study qualitatively support the observations by fishermen of a wind‐induced effect on lobster catch rates.     

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

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

A two-chambered trap reduces within-trap predation by octopus on rock lobsters in aquarium trials

A two-chambered lobster trap was developed that in aquarium trials significantly (p < 0.01) reduced octopus predation on trap-caught spiny lobster. The trap was designed using information gained from an investigation of the behavioural interactions of the maori octopus (Octopus maorum) with traps used in the South Australian commercial lobster (Jasus edwardsii) fishery. This study showed that octopuses were primarily attracted to traps by the presence of bait as opposed to lobsters and that octopus entry into traps was ‘fortuitous’ and mediated by speculative exploration. The outer chamber of the modified trap contained bait and allowed entry by octopuses but not lobster and the inner chamber allowed access to both animals. The trap worked on the principle that octopuses would enter the outer chamber containing bait via a side entrance in preference to entry to the inner chamber containing lobsters via the neck. This was found to be the case and lobster mortality was 70% lower in the two-chambered trap than a standard trap. Successful adaptation of this trap design to commercial fishing conditions could significantly reduce rates of octopus predation on rock lobsters in several important southern hemisphere fisheries for spiny lobsters.     

Diets of top predators indicate pelagic juvenile rockfish (Sebastes spp.) abundance in the California Current System

Diets of top predators may be useful indicators to the availability of forage fish in marine ecosystems. Juvenile rockfish (young‐of‐the‐year Sebastes spp.) compose a significant part of the diet for many predators in the central California Current, including chinook salmon (Oncorhynchus tshawytscha), and several species of marine birds and mammals. Herein, we develop annual indices of juvenile rockfish relative abundance by collating time series data sets on: (i) the proportion of rockfish in the diet of three species of seabirds breeding on Southeast Farallon Island (1975–2002); (ii) the number of rockfish in chinook salmon stomachs (1980–99); and (iii) the abundance of rockfish captured in scientific mid‐water trawl net surveys (1983–2002). We used Principal Component Analysis (PCA) to combine indices, and refer to these as ‘Multivariate Rockfish Indices’ (MRI). Combining time series verifies the patterns shown by each alone and provides a synoptic perspective on juvenile rockfish relative abundance. The diets of predators with the largest foraging ranges (Common Murre, Uria aalge) and chinook salmon co‐varied strongly with the net samples, and appear to be the best indicators. The salmon also sampled species of Sebastes not caught in the nets. The MRI reveals interannual variability in juvenile rockfish abundance, a substantial decline in abundance in the 1990s, and a partial recovery in the early 2000s. Predator‐based sampling is a cost‐effective enhancement of scientific net sampling.     

Mitigating sea turtle by-catch in coastal passive net fisheries

There is growing evidence that small-scale, coastal, passive net fisheries may be the largest single threat to some sea turtle populations. We review assessments of turtle interactions in these fisheries, and experiments on gear-technology approaches (modifying gear designs, materials and fishing methods) to mitigate turtle by-catch, available from a small number of studies and fisheries. Additional assessments are needed to improve the limited understanding of the relative degree of risk coastal net fisheries pose to turtle populations, to prioritize limited conservation resources and identify suitable mitigation opportunities. Whether gear technology provides effective and commercially viable solutions, alone or in combination with other approaches, is not well-understood. Fishery-specific assessments and trials are needed, as differences between fisheries, including in gear designs; turtle and target species, sizes and abundance; socioeconomic context; and practicality affect efficacy and suitability of by-catch mitigation methods. Promising gear-technology approaches for gillnets and trammel nets include: increasing gear visibility to turtles but not target species, through illumination and line materials; reducing net vertical height; increasing tiedown length or eliminating tiedowns; incorporating shark-shaped silhouettes; and modifying float characteristics, the number of floats or eliminating floats. Promising gear-technology approaches for pound nets and other trap gear include: replacing mesh with ropes in the upper portion of leaders; incorporating a turtle releasing device into traps; modifying the shape of the trap roof to direct turtles towards the location of an escapement device; using an open trap; and incorporating a device to prevent sea turtle entrance into traps.     

Influences of twine diameter and mesh area on the efficiency and durability of baited hoop nets targeting portunids

The utility of varying twine diameter (0.5–0.8 mm Ø) and/or mesh area (0.5:1) in south‐eastern Australian recreational hoop nets was assessed in response to concerns over (1) impacts to discarded, undersize Scylla serrata L. and Portunus pelagicus Forskål and (2) marine debris (lost meshes). There was a negative relationship between Ø and breakage, with more in the narrowest (16.16–18.42 meshes deployment^?1) than thickest (8.79–4.68) twines. Mesh damage was also affected by interactions between netting area and (1) soak time (only S. serrata) and (2) catches, with all nets similarly damaged during <3.5‐h soaks, or when only one crab was caught, beyond which the large‐area nets incurred more. Irrespective of net, there were consistent positive relationships between mesh damage and water temperature, and more damage overnight. Large crabs took longer to remove, but more so from thicker‐twined and large‐area nets, and some also sustained the most damage. Twine diameter did not affect S. serrata catches, but was negatively associated with catches of P. pelagicus, while the small‐area nets caught proportionally (to area) fewer portunids. The results reflect species‐ and size‐specific behavioural variability, but support using thick twine and limiting deployment durations for hoop nets. Alternatively, other less controversial traps might offer a more holistic solution to the stated concerns.     

Relationship between soak time and number of enmeshed animals in experimentally lost gill nets

In order to determine the effects of ghost fishing by lost gill nets, the relationship was examined between soak time and number of enmeshed animals in experimentally lost gill nets by using diving observations. Two experimental gill nets were set at 13 m depth in Tateyama Bay, Chiba Prefecture, Japan for approximately 200 days. One gill net was deployed in a small trough surrounded by artificial reefs, and the other was deployed on an adjacent open sandy bed. Twelve species of crustaceans, six species of gastropods, and five species of bony fish were enmeshed in the experimental gill nets. The number of enmeshed animals in the artificial reef gill net was substantially larger than that in the sandy bed gill net. The number of enmeshed animals in the experimental gill nets increased rapidly within one month after deployment, and then declined gradually showing fluctuations caused by the decrease in newly enmeshed animals, and the drop off from gill nets caused by the decomposition of dead animals. The decrease in the number of enmeshed animals was expressed by logarithmic equations, and based on these equations, the duration of capture function for the lost gill nets was calculated to be 284–561 days in the artificial reef gill net and 200 days in the sandy bed gill net. The duration of capture function for the lost gill nets for non-commercial by-catch species such as small crustaceans and gastropods was longer than for commercial species such as Japanese spiny lobster and bony fish.     

Cost–benefit analysis of two culture methods that influence pearl production from the black‐lip pearl oyster,Pinctada margaritifera

The black‐lip pearl oyster, Pinctada margaritifera, used for round pearl production in Polynesia, is generally cultured using “ear‐hanging” where they are attached to a rope to form “chaplets.” In other countries, pearl oysters are cultured using panel (pocket) nets that are more expensive than chaplets but afford more protection to cultured oysters. Prior research has shown panel nets produce pearls of higher quality and value, potentially generating higher profits. This study used cost–benefit analysis to compare pearl production using chaplet‐based and panel net‐based culture methods. Whole farm data, including gross revenues and annual production costs, fixed and variable, were analyzed. Average production cost per pearl using panel net‐based culture was USD 22.47 and for chaplet‐based culture was USD 21.55. However, use of panel nets saved around 3,430 hr (USD 6,860) of labor a year, offsetting the greater capital investment. A chaplet‐based pearl farm generated USD 65,738 in annual profits compared to USD 88,774 for a panel net‐based farm. Positive cash flow was achieved 1 year earlier (Year 7) for the panel net‐based farm. This is the first economic analysis of different pearl culture methods for P. margaritifera and evidence of profitability will support further development of the black‐lip pearl industry in the Indo‐Pacific region.     

Dependence of recruitment on parent stock of the spiny lobster,Panulirus argus,in Florida

Despite management practices to achieve sustainability, commercial landings for Florida spiny lobster (Panulirus argus) have experienced a drastic decline (57%) since 2000. This is cause for concern not only for economic reasons, but for issues of sustainability. An annual index of P. argus post‐larval (puerulus) abundance, estimated with a generalized linear model with significant mean sea‐level effects, shows a 36% decrease in annual puerulus supply since 1988. In addition, local Florida spawning stock biomass estimated from an age‐structured sequential population analysis decreased 57% since 1988. Puerulus abundance follows a highly correlated (R = 0.76) trend with a 12‐month delayed spawning stock abundance, which supports the contention that the Florida spawning population is a significant contributing factor to post‐larval recruitment in Florida. Residuals about the puerulus on spawning stock abundance function follow closely an interannual North Atlantic Oscillation Index signal. This residual effect is thought of as a secondary regional population effect on Florida puerulus recruitment. The Florida spiny lobster stock is exploited with no fishing mortality controls due to the Pan Caribbean recruitment concept adopted in Florida spiny lobster management. Therefore, the potential of recruitment overfishing exists if fishing mortality controls to protect local spawning stock abundance, such as catch quotas, are not introduced.     

Effects of trap fishing on reef fish communities

• 1. Trap fishing is widespread on coral reefs but the sustainability of this practice is causing concern because it is efficient and unselective. The effects of trap fishing were investigated by comparing fish assemblages among six Caribbean islands subject to different trapping pressures. These ranged from none in Bonaire and Saba increasing through Puerto Rico, St Lucia, Dominica and Jamaica respectively.
• 2. Fish were censused at depths of 5 m and 15 m on fore‐reef slopes by counting the numbers within replicate 10 m diameter areas for 15 min. Between 64 and 1375 counts were made in each country.
• 3. In St Lucia and Jamaica abundance of fish censused on the reef was compared to representation in traps which were visually sampled underwater in the area of fish counts. Twenty‐three traps were sampled in Jamaica and 75 in St Lucia. For some comparisons between these islands, St Lucian sampling effort was reduced to that of Jamaica (23 traps and 112 counts) by randomly sub‐sampling 10 times.
• 4. Traps contained 54 different species in St Lucia and 22 in Jamaica, while there were 90 and 57 respectively in counts. After reducing St Lucian sampling effort to Jamaican levels, an average of 35 species were found in traps and 70 seen in counts. Of these, 76% in St Lucia and 73% in Jamaica were relatively more abundant in traps than they were on the reef.
• 5. Species were considered to be highly susceptible to trapping if the ratio of their abundance in traps compared to that on the reef exceeded 3:1. Trapping pressure was approximately three and a half times greater in Jamaica than St Lucia. After equalizing sampling effort, there was an average of 16 highly trappable species in St Lucia compared to 13 in Jamaica. Species did not always appear highly trappable in both countries. Eleven of St Lucia's highly trappable species were absent from Jamaica (falling to 8.5 on average after equalizing sampling effort), but none vice versa, suggesting that trapping may have contributed to their absence or rarity on Jamaican reefs.
• 6. The Tetraodontiformes, which include many non‐target species, were particularly susceptible to trapping in both countries. Their abundance in the six islands censused was inversely related to trap fishing pressure, as was that of two other non‐target families, butterflyfish (Chaetodontidae) and angelfish (Pomacanthidae).
• 7. To determine whether fish that are common in traps in St Lucia are reaching sexual maturity before capture, size frequency data for 23 species from a sample of trap catches were gathered and examined for their state of maturity. In seven species, more than a third of 705 trapped fish were immature, indicating that trap fishing causes growth over‐fishing (premature removal of fish), and calling into question the sustainability of yields for these species.
• 8. In conclusion, at the intensities seen in this study, trap fisheries cause serious over‐fishing, reduce biodiversity, and alter ecosystem structure. While commonly perceived as low impact, coral reef trap fisheries in the Caribbean and further afield, need tighter regulation and control.

Copyright © 2006 John Wiley & Sons, Ltd.     

灯光诱集对中小型浮游动物群落的生态学效应

2014年5月21—23日和27日在南沙群岛中部海域开展灯光罩网作业的同时,开展诱集前后中小型浮游动物群落变化的初步实验,研究浮游动物群落对灯光反应的敏感性,灯光对群落产生了较为明显的生态学效应。诱集前后共出现浮游动物178种,隶属16个类群。诱集后种类数增加,种类组成的更替率为41%。各类群中,除枝角类外其余15个类群在诱集前后出现的种类均发生变化;除原生动物在诱集后种类数下降外,其他类群的种类数均呈增加的趋势。浮游动物绝大部分类群对灯光诱集较为敏感,趋光性有正有负。诱集前后浮游动物优势种组成发生一定的变化,更替率为50%。诱集前优势种以桡足类为主,而诱集后有尾类的优势地位明显增强。诱集后浮游动物优势种优势度和出现频率均呈明显降低的趋势。南沙群岛海域中小型浮游动物优势种诱集前后均呈聚集分布,各优势种对灯光反应敏感,不同种类对灯光的适应性有所差异。住囊虫等大部分种类对灯光的适应性较强,诱集后聚集强度明显增加;而驼背大眼水蚤和活泼大眼剑水蚤诱集后聚集强度明显下降。桡足类幼虫和小纺锤水蚤等诱集后,聚集强度明显上升,之后又大幅下降。浮游动物生物量和栖息密度在诱集后总体呈明显的增加趋势,以诱集初期增幅最大,之后数量虽有所降低,但仍高于诱集前。灯光可使浮游动物物种丰富度和多样性水平明显提高,但尚未改变浮游动物的群落结构。浮游动物对人造光反应的种间和类群间差异,是由生物自身的生理特征和不同的摄食策略决定的。诱集后游泳生物摄食强度提高,导致了诱集后期浮游动物数量下降。     

Reactions of temperate reef fish larvae to boat sound

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Pinger affects fish catch efficiency and damage to bottom gill nets related to bottlenose dolphins

There is some evidence that the presence of Tursiops truncatus in fishing areas represents a real economic threat to fishermen due the dolphin feeding on the entangled fish, damaging the nets and reducing the fish catch. We have carried out experiments to assess the efficiency of a pinger in decreasing the interaction between the dolphins and fishing nets, in a fishing area off the coast of southern Italy, where Tursiops truncatus is frequently observed to interact with bottom gill nets. Two identical monofilament bottom gill nets (900 m long), one equipped with pingers and the other without, were used to measure the effect of these pingers on the abundance of the catch and net damage. For each haul (58 in total), data on dolphin sightings near the nets, damage judged to have been done by dolphins, weight and species composition of the catch were collected. All damage to the nets were recorded at the end of each haul. Dolphins in the fishing area were sighted 11 times out of 29 fishing activities (38%). The net equipped with pingers contained 28% more fish (biomass) than the net without pingers (t test, P < 0.04) and was less damaged (−31%, t test, P < 0.01). To assess whether the efficacy of these pingers remain constant over long period, long-term experiments should be carried out.     

Using logbook-based catch-rate data to detect yellow eel population trends in the southern Baltic Sea

Within recent years, a slight but significant increase of European eel Anguilla anguilla (L.) recruitment has been documented, but it remains questionable whether or not the increased recruitment levels resulted in higher eel numbers at the regional scale. To detect the changes in yellow eel numbers, logbook data covering a 15-year time series of catch per unit effort (CPUE) data from the German Baltic Sea were analysed. Monthly mean catch rates were calculated for two different size classes for two passive gears: fyke and stationary trap nets. Change-point analysis was applied to discover changes in the catch data. After a period of decreasing or constant catch rates, the fyke net data indicated that yellow eel numbers increased slightly in recent years in the Baltic Sea. Besides increasing numbers of immigrating juvenile eels, other population dynamics or conservation efforts might have added to the observed positive stock trend.     

Catching invasive Chinese mitten crabs while releasing the endangered European eel and other fish by‐catch: The implications of fyke net design

1. Modifications of a traditional fyke net design were trialled in 42 hauls over 5 months at 42 locations in the Thames estuary, London. These trials were to determine whether the modified nets could be used to catch invasive mitten crabs while at the same time releasing endangered eels, back into the river.
2. The modifications included rings of different diameters fixed into the netting to provide escape apertures and also a variation in mesh size. A standard, unmodified net was included as a control.
3. Captured mitten crabs, eels and other fish by‐catch were measured and recorded for all deployed nets. Mitten crabs and eels were caught in all nets except those of the largest mesh size (70 mm) which caught no eels. This may have been the combined effect of the mesh size and it being set on the square, versus the normal diagonal netting which may become increasingly constricted in one axis, under tension. Such a square mesh net could be used to trap crabs of carapace width > 65 mm, while releasing all eels.
4. The smallest rings, 22 mm internal diameter, inserted into the mesh may have allowed the escape of eels < 35 cm length, but retained larger, market legal, individuals. This suggests that a slightly smaller escape ring could potentially be used to release eels of ≤ 30 cm in length, in line with current regulations.

     

Escape vents and trap selectivity in the fishery for the Juan Fernández rock lobster (Jasus frontalis), Chile

To develop ways to catch fewer undersized specimens of Jasus frontalis in the traps of the rock lobster fishery off the Juan Fernández Archipelago (Chile), we studied the use of lobster traps with different-sized escape vents (circular windows of 80, 85, or 90 mm diameter). The traps used in the present fishery served as controls. Selection curves were fit to each of the vent sizes examined in the study. The method of alternating hauls was used for this purpose in a manner similar to that employed with trawl nets. We compared the size–frequency distributions obtained for each vent size with those determined for the control traps. We monitored 2437 traps and obtained a total catch of 13,444 specimens. Undersized individuals decreased in the catch as the diameter of the openings increased. The selection curves fit a logistic-type model adequately. A direct relationship was established between the vent size and the length corresponding of the first catch (L₅₀). The CPUE for legal-sized rock lobster increased in traps having up to 85-mm vents, but this yield dropped in traps fitted with 90-mm vents. The CPUE for undersized rock lobster, however, was inversely proportional to the size of the vents. Unlike typical selectivity literature that relies on the L₅₀, the objective of this study was to maximize the number of legal (≥98 mm Lc) specimens retained in the traps while simultaneously minimizing the retention of undersized specimens. To achieve this, we used a model relating vent size to L₅₀ and the slope of the selection ogives. The optimal diameter for vents in this fishery was determined to be 83 mm. Furthermore, underwater recordings were used to register the escape behavior of the lobsters. These recordings contributed new data on the way in which the lobsters detect, confront, and escape through the vents.     

Reducing the mortality of freshwater turtles in commercial fish traps

• 1. Mortality of air‐breathing vertebrates has been recognized for some time as a significant risk in Australian inland fisheries. There has often been conflict between the desires of fishers to maximize catches of their target species and the implementation of effective methods to reduce nontarget bycatch.
• 2. Two trials were conducted to evaluate the effectiveness of modifications to fish traps designed to prevent the capture of freshwater turtles (Emydura macquarii) and to facilitate their release. The first study evaluated the use of 100 mm exclusion rings to prevent turtles entering eel traps. The second study assessed two configurations of a carp trap designed to release the accidental catch of turtles.
• 3. Eel traps fitted with 100 mm exclusion rings significantly reduced the turtle bycatch, with no significant difference being observed between mean size of eels captured in traps fitted with exclusion rings and traps without rings.
• 4. The trials on the modified carp trap confirmed that they effectively retained carp and released a majority (77%) of turtles over a 4 h period. Turtles retained in the carp traps were significantly longer than those that found their way out of the trap.
• 5. This study demonstrates the different approaches that can be taken to achieve a reduction in non‐target bycatch associated with traps, and illustrates the importance of exploiting both the physical and behavioural differences of the target and non‐target species in order to develop appropriate gear designs that effectively restrict the entry, or facilitate the release, of bycatch species.

Copyright © 2004 John Wiley & Sons, Ltd.     

Striking a balance between retaining populations of protected seahorses and maintaining swimming nets

• 1. The fish family Syngnathidae (seahorses, pipefish, pipehorses and seadragons) is fully protected in New South Wales, Australia, but in some countries certain species are threatened by unsustainable collecting, capture as incidental bycatch, and habitat degradation.
• 2. Within Sydney Harbour, two species of seahorses (Hippocampus abdominalis and Hippocampus whitei) have been found to colonize artificial structures such as jetty pylons and protective netted swimming enclosures. These protective nets are subject to fouling from epibiotic growth (algae, ascidians, bryozoans, etc.) and rubbish, which causes the nets to collapse from the additional weight. Local authorities employ diving contractors on an ad hoc basis to remove the epibiota from nets.
• 3. Surveys showed a significant decline in the numbers of both seahorse species at one site following the replacement of a net, and recovery of the H. whitei population took more than 15 months.
• 4. A manipulative experiment tested the importance of epibiotic growth for seahorses. H. whitei, tagged with individual marks, were allocated to sections of a net that had undergone different cleaning procedures. Seahorse size, position on the net and total population abundance were recorded every 2 weeks over a 3 month period. It was demonstrated that seahorses have a significant positive association with epibiotic growth and proximity to the sea floor. Seahorse populations also showed seasonal variation in abundance with increased numbers on the net during the breeding season (spring–summer).
• 5. This project has led to the development of best practice net cleaning procedures for local authorities in Sydney Harbour to manage growth on the nets while minimizing impacts on seahorse populations. Copyright © 2009 John Wiley & Sons, Ltd.

     

Incidental capture of Caretta caretta in trammel nets off the western coast of Sardinia (Italy): statistical models of capture abundance and immediate survival

• 1. Trammel nets are one important cause of sea turtle mortality resulting from incidental capture. This study presents findings over a 10‐year period during which loggerhead turtle by‐catch in trammel nets, set off the central west coast of Sardinia (Italy) in the summer months, was recorded by 17 fishing vessels.
• 2. Since the by‐catch registered represented counts of a rare event, data from the 17 vessels were used in the zero‐inflated Poisson (ZIP) model to determine the abundance of turtle by‐catch in trammel nets of the entire fleet, while a binomial generalized linear model was used to assess the probability of immediate survival for sea turtles incidentally caught in this gear.
• 3. The ZIP model quantified in about 45% the probability that 0.6 turtles have been caught by each vessel using trammel nets during summer over the 10‐year period. In addition, the model estimated a total of 916 by‐catch if the entire small‐scale fleet was to use trammel nets in the study area in the summers between 1992 and 2001, with a direct mortality rate of 69%.
• 4. The probability of immediate survival for sea turtles caught in trammel nets seems to be directly related to the size of the specimens caught; however, this relationship is plausible only when incidental capture in the net occurs shortly before gear retrieval.
• 5. The study area represents a region where the abundance of sea turtle by‐catch per vessel in trammel nets was much higher in July and August than in June and could represent a potential hot spot for the presence of juvenile loggerhead turtles, with high levels of interactions between the species and this fishing gear. Further research should better characterize the incidents of by‐catch and assess potential innovative solutions that allow small‐scale fisheries to coexist alongside sea turtles. Copyright © 2010 John Wiley & Sons, Ltd.