FIELD EXPERIMENTS SHOW THAT ACOUSTIC PINGERS REDUCE MARINE MAMMAL BYCATCH IN THE CALIFORNIA DRIFT GILL NET FISHERY

A controlled experiment was carried out in 1996–1997 to determine whether acoustic deterrent devices (pingers) reduce marine mammal bycatch in the California drift gill net fishery for swordfish and sharks. Using Fisher's exact test, bycatch rates with pingers were significantly less for all cetacean species combined ( P < 0.001) and for all pinniped species combined ( P = 0.003). For species tested separately with this test, bycatch reduction was statistically significant for short-beaked common dolphins ( P = 0.001) and California sea lions ( P = 0.02). Bycatch reduction is not statistically significant for the other species tested separately, but sample sizes and statistical power were low, and bycatch rates were lower in pingered nets for six of the eight other cetacean and pinniped species. A log-linear model relating the mean rate of entanglement to the number of pingers deployed was fit to the data for three groups: short-beaked common dolphins, other cetaceans, and pinnipeds. For a net with 40 pingers, the models predict approximately a 12-fold decrease in entanglement for short-beaked common dolphins, a 4-fold decrease for other cetaceans, and a 3-fold decrease for pinnipeds. No other variables were found that could explain this effect. The pinger experiment ended when regulations were enacted to make pingers mandatory in this fishery.     

Patterns of Dolphin Bycatch in a North-Western Australian Trawl Fishery

The bycatch of small cetaceans in commercial fisheries is a global wildlife management problem. We used data from skippers'' logbooks and independent observers to assess common bottlenose dolphin (Tursiops truncatus) bycatch patterns between 2003 and 2009 in the Pilbara Trawl Fishery, Western Australia. Both datasets indicated that dolphins were caught in all fishery areas, across all depths and throughout the year. Over the entire datasets, observer reported bycatch rates (n = 52 dolphins in 4,124 trawls, or 12.6 dolphins/1,000 trawls) were ca. double those reported by skippers (n = 180 dolphins in 27,904 trawls, or 6.5 dolphins/1,000 trawls). Generalised Linear Models based on observer data, which better explained the variation in dolphin bycatch, indicated that the most significant predictors of dolphin catch were: (1) vessel - one trawl vessel caught significantly more dolphins than three others assessed; (2) time of day – the lowest dolphin bycatch rates were between 00:00 and 05:59; and (3) whether nets included bycatch reduction devices (BRDs) - the rate was reduced by ca. 45%, from 18.8 to 10.3 dolphins/1,000 trawls, after their introduction. These results indicated that differences among vessels (or skippers'' trawling techniques) and dolphin behavior (a diurnal pattern) influenced the rates of dolphin capture; and that spatial or seasonal adjustments to trawling effort would be unlikely to significantly reduce dolphin bycatch. Recent skipper''s logbook data show that dolphin bycatch rates have not declined since those reported in 2006, when BRDs were introduced across the fishery. Modified BRDs, with top-opening escape hatches from which dolphins might escape to the surface, may be a more effective means of further reducing dolphin bycatch. The vulnerability of this dolphin population to trawling-related mortality cannot be assessed in the absence of an ongoing observer program and without information on trawler-associated dolphin community size, broader dolphin population size and connectivity with adjacent populations.     

Subsurface behavior of bottlenose dolphins (Tursiops truncatus) interacting with fish trawl nets in northwestern Australia: Implications for bycatch mitigation

Most studies of delphinid‐trawler interactions have documented the surface behavior of dolphins feeding on discarded bycatch, but not their subsurface behavior around demersal trawl gear. Using video cameras mounted inside trawl nets, we recorded the subsurface behavior of common bottlenose dolphins (Tursiops truncatus) in a demersal fish trawl fishery in northwestern Australia. Footage from 36 trawls across the fishery was analyzed to determine the extent of dolphin‐gear interactions and the behavior of dolphins inside the nets. Interaction rates were high, with dolphins present inside and outside the nets during 29 and 34 trawls, respectively, and for up to 99% of the trawl duration. The proportion of foraging behaviors exhibited inside the nets was higher than the proportions of traveling and socializing behaviors. Twenty‐nine individuals were identified inside the net, seven of which returned repeatedly within and between trawls and fishing trips, but were observed primarily in the same localized areas in which they were first recorded. Our results suggest that entering trawl nets may be a frequently occurring, yet specialized behavior exhibited by a small subset of trawler‐associated dolphins. We propose that gear modifications, not spatial or temporal adjustments to fishing effort, have the greatest potential to reduce dolphin bycatch.     

Conflict between Dolphins and a Data-Scarce Fishery of the European Union

Fisheries depredation by marine mammals is an economic concern worldwide. We combined questionnaires, acoustic monitoring, and participatory experiments to investigate the occurrence of bottlenose dolphins in the fisheries of Northern Cyprus, and the extent of their conflict with set-nets, an economically important metier of Mediterranean fisheries. Dolphins were present in fishing grounds throughout the year and were detected at 28% of sets. Net damage was on average six times greater where dolphins were present, was correlated with dolphin presence, and the associated costs were considerable. An acoustic deterrent pinger was tested, but had no significant effect although more powerful pingers could have greater impact. However, our findings indicate that effective management of fish stocks is urgently required to address the overexploitation that is likely driving depredation behaviour in dolphins, that in turn leads to net damage and the associated costs to the fisheries.     

Technical mitigation to reduce marine mammal bycatch and entanglement in commercial fishing gear: lessons learnt and future directions

Fisheries bycatch is one of the biggest threats to marine mammal populations. A literature review was undertaken to provide a comprehensive assessment and synopsis of gear modifications and technical devices to reduce marine mammal bycatch in commercial trawl, purse seine, longline, gillnet and pot/trap fisheries. Successfully implemented mitigation measures include acoustic deterrent devices (pingers) which reduced the bycatch of some small cetacean species in gillnets, appropriately designed exclusion devices which reduced pinniped bycatch in some trawl fisheries, and various pot/trap guard designs that reduced marine mammal entrapment. However, substantial development and research of mitigation options is required to address the bycatch of a range of species in many fisheries. No reliably effective technical solutions to reduce small cetacean bycatch in trawl nets are available, although loud pingers have shown potential. There are currently no technical options that effectively reduce marine mammal interactions in longline fisheries, although development of catch and hook protection devices is promising. Solutions are also needed for species, particularly pinnipeds and small cetaceans, that are not deterred by pingers and continue to be caught in static gillnets. Large whale entanglements in static gear, particularly buoy lines for pots/traps, needs urgent attention although there is encouraging research on rope-less pot/trap systems and identification of rope colours that are more detectable to whale species. Future mitigation development and deployment requires rigorous scientific testing to determine if significant bycatch reduction has been achieved, as well as consideration of potentially conflicting mitigation outcomes if multiple species are impacted by a fishery.

     

Characteristics of Fishing Operations,Environment and Life History Contributing to Small Cetacean Bycatch in the Northeast Atlantic

Fisheries bycatch is a key threat to cetacean species globally. Managing the impact requires an understanding of the conditions under which animals are caught and the sections of the population affected. We used observer data collected on an albacore tuna gillnet fishery in the northeast Atlantic, to assess operational and environmental factors contributing to bycatch of common and striped dolphins, using generalised linear models and model averaging. Life history demographics of the captured animals were also investigated. In both species, young males dominated the catch. The age ratio of common dolphins was significantly different from that estimated for the population in the region, based on life tables (G = 17.1, d.f. = 2, p = 0.002). Skewed age and sex ratios may reflect varying vulnerability to capture, through differences in behaviour or segregation in populations. Adult females constituted the second largest portion of the bycatch for both species, with potential consequences for population sustainability. Depth was the most important parameter influencing bycatch of both species and reflected what is known about common and striped dolphin habitat use in the region as the probability of catching common dolphins decreased, and striped dolphins increased, with increasing depth. Striped dolphin capture was similarly influenced by the extent to which operations were conducted in daylight, with the probability of capture increasing with increased operations in the pre-sunset and post-sunrise period, potentially driven by increased ability of observers to record animals during daylight operations, or by diurnal movements increasing contact with the fishery. Effort, based on net length and soak time, had little influence on the probability of capturing either species. Our results illustrate the importance of assessing the demographic of the animals captured during observer programmes and, perhaps more importantly, suggest that effort restrictions alone may not be sufficient to eradicate bycatch in areas where driftnets and small cetaceans co-occur.     

Harbor porpoise (Phocoena phocoena) reactions to pingers

The use of acoustic alarms (pingers) has been mandated in several gill net fisheries around the world. Even though pingers have shown to reduce the incidental catch there are still questions to be answered in relation to effective range, habituation and displacement. In the present studies, the vocalization behavior of porpoises was recorded in response to two different pingers, AQUAmark100 (20–160 kHz) and AQUAmark300 (10 kHz). The Scottish experiment included an AQUAmark100 pinger running in on/off cycles. The pinger was placed in an array of acoustic click detectors (C‐PODs) spaced at different distances from the pinger. In Denmark, three experiments were conducted. One had the same AQUAmark100 pinger placed in a C‐POD array. The second and third experiment used an AQUAmark300 pinger running in on/off cycles. Both trial results of the AQUAmark100 revealed significant pinger reduction effects at 0, 200, and 400 m distance; however, the vocalization behavior reveal no signs of habituation. The studies of the AQUAmark300 revealed a significant pinger effect at 0 m distance and either none or 17% reduction at 300 m distance. At one station, however, habituation effects were found indicated by an increase in clicks over time. These results are important in relation to pinger use and thus fisheries management.     

Changes in fish bycatch during the shrimp fishing season along the eastern coast of the mouth of the Gulf of California

One of the main concerns of shrimp fisheries is the associated impact on ecosystem biodiversity, particularly on fish assemblages that are poorly characterized yet likely very relevant to the health of the ecosystem. The continental shelf along the eastern coast of the mouth of the Gulf of California is a region of high biodiversity that harbors highly productive fisheries. This study aimed to analyze the changes in the soft bottom fish assemblages caught as bycatch in the shrimp fishery located in this region. Sampling was conducted with commercial trawls at 16 fixed stations during the 2006–2007 shrimp‐fishing season. A total of 103 fish species from 80 genera and 47 families were collected. The ecological and taxonomic diversity as well as the composition and abundance of the fish community caught as bycatch in the shrimp trawl fishery were found to be significantly different in the autumn and winter. Ordination and similarity analyses also revealed differing patterns. Species abundance was strongly associated with sea bottom temperature, depth and latitude. The effects of these abiotic variables on the observed diversity patterns and the possible influences of the fishery are discussed.     

Catch composition of drift gillnets in a multi-species fishery with an emphasis on kingfish (Scomberomorus commerson) in Northern Persian Gulf

Gillnets are the primary fishing gear used in tropical multi-species fisheries along the Iranian southern coastal waters. Therefore, it is necessary to investigate the catch composition and performance of fishing gear for the possible negative effects on the stocks. Catch data and length frequency distribution (just for Kingfish, S. commerson) were examined for three kinds of drift gillnets: 1) small-meshed nets, 2) medium-meshed nets, and 3) nets with a single mesh size of 165 mm. This study was conducted in the northern part of the Persian Gulf from 2014 to 2015. Overall, 60 species of 32 families from four fish groups (i.e., Pelagic, Demersal, Benthopelagic, and Reef-associated) were recorded. Each net-type was used to target more than one species, with most species being considered as bycatch. Commercial fish species were caught the most, accounting for around 83% of the total catches. S. commerson is targeted by all kinds of nets, with medium-meshed nets being most efficient. The majority of S. commerson caught by the nets were immature. Overall, the total ban of gillnets with small mesh sizes is recommended to protect young S. commerson and prevent the possible risk of growth overfishing. Studies on gillnet selectivity are needed to set minimum mesh regulations for S. commerson and other commercial species if the potential impacts of gillnet are known.     

Bycatch quotas in the Gulf of Mexico shrimp trawl fishery: can they work?

Bycatch of unwanted, prohibited, or protected species is a problem in most commercial fisheries. Trawl fisheries are particularly prone to bycatch problems because trawls are not species-selective. In this paper, I review the history of finfish bycatch research in the Gulf of Mexico shrimp trawl fishery and explore the use of quotas to reduce finfish bycatch by examining four fisheries that currently use bycatch quotas: (1) the arrow squid trawl fishery of New Zealand, which uses fleet bycatch quotas for sea lion bycatch, (2) the Alaskan groundfish trawl fisheries, which use fleet quotas under a vessel incentive program for prohibited species, (3) the groundfish trawl fishery of British Columbia, Canada which uses individual vessel bycatch quotas for prohibited species, and (4) the multi-species trawl fisheries of New Zealand, which use catch balancing, or individual transferable quotas, for most commercially landed species. Based on the bycatch quota experiences in these fisheries, elements of successful bycatch quota programs include: (1) individual accountability, in the form of individual or cooperative bycatch quotas, rather than fleet quotas, (2) 100% observer coverage, (3) relatively small, manageable fleets, (4) limited landing ports that can be easily monitored, particularly if observer coverage is incomplete, (5) reliable enforcement, (6) penalties that are true disincentives, and (7) some flexibility in the system for fishermen to have alternatives to manage their bycatch. The Gulf of Mexico shrimp trawl fishery, with an estimated 20,000 licensed boats, is currently too large for individual bycatch quotas to be practical, although individual or cooperative bycatch quotas would be excellent strategies for reducing the bycatch of a smaller fleet. Mobile closed areas might be beneficial for reducing the bycatch of particular species, but these short-term closures would require real-time monitoring of bycatch rates and vessel monitoring systems on all vessels. However, under any management regime, incentives and/or rigorously enforced disincentives are the key to successful bycatch reduction.     

Bycatch and strandings programs as ecological indicators for data-limited cetaceans

An integrated approach of using strandings and bycatch data may provide an indicator of long-term trends for data-limited cetaceans. Strandings programs can give a faithful representation of the species composition of cetacean assemblages, while standardised bycatch rates can provide a measure of relative abundance. Comparing the two datasets may also facilitate managing impacts by understanding which species, sex or sizes are the most vulnerable to interactions with fisheries gear. Here we apply this approach to two long-term datasets in East Australia, bycatch in the Queensland Shark Control Program (QSCP, 1992–2012) and strandings in the Queensland Marine Wildlife Strandings and Mortality Program (StrandNet, 1996–2012). Short-beaked common dolphins, Delphinus delphis, were markedly more frequent in bycatch than in the strandings dataset, suggesting that they are more prone to being incidentally caught than other cetacean species in the region. The reverse was true for humpback whales, Megaptera novaeangliae, bottlenose dolphins, Tursiops spp.; and species predominantly found in offshore waters. QSCP bycatch was strongly skewed towards females for short-beaked common dolphins, and towards smaller sizes for Australian humpback dolphins, Sousa sahulensis. Overall, both datasets demonstrated similar seasonality and a similar long-term increase from 1996 until 2008. Analysis on a species-by-species basis was then used to explore potential explanations for long-term trends, which ranged from a recovering stock (humpback whales) to a shift in habitat use (short-beaked common dolphins).     

Effect of artificial baits on the catch efficiency of monofilament gill nets

Greater success in catching fish with gill nets is possible if more the fish are attracted to the nets. Bait has been successfully used to lure fish into the gill nets. With the aim of increasing the catch efficiency of monofilament gill nets, a study was conducted between January 2009 and December 2010 to test the effect of artificial baits on the efficiency of 40, 50 and 55 mm monofilament gill nets in the Keban Dam Lake (Elaz??/Turkey). The catch rate of the baited nets was compared to similar nets without bait. Baited nets caught 482 fish (71.8% of the total, seven species). Non‐baited nets caught 189 fish (28% of the total, seven species). The majority of fish (238) were caught using baited gill nets with 40 mm mesh. The most commonly caught species was Capoeta trutta. The differences between the baited gill nets and non‐baited gill nets were statistically significant (P < 0.05). Finally, it was understood that artificially baited monofilament gill nets had higher catch efficiencies than non‐baited monofilament gill nets. Unlike most natural baits, artificial baits are re‐usable and thus more economical in the long term.     

Developing ultraviolet illumination of gillnets as a method to reduce sea turtle bycatch

Fisheries bycatch of marine animals has been linked to population declines of multiple species, including many sea turtles. Altering the visual cues associated with fishing gear may reduce sea turtle bycatch. We examined the effectiveness of illuminating gillnets with ultraviolet (UV) light-emitting diodes for reducing green sea turtle (Chelonia mydas) interactions. We found that the mean sea turtle capture rate was reduced by 39.7% in UV-illuminated nets compared with nets without illumination. In collaboration with commercial fishermen, we tested UV net illumination in a bottom-set gillnet fishery in Baja California, Mexico. We did not find any difference in overall target fish catch rate or market value between net types. These findings suggest that UV net illumination may have applications in coastal and pelagic gillnet fisheries to reduce sea turtle bycatch.     

Bycatch species composition over time by tuna purse-seine fishery in the eastern tropical Atlantic Ocean

Within the Ecosystem-based fisheries management framework, we evaluated the changes over time in bycatch species of the European tuna purse-seine fishery operating in the eastern Atlantic Ocean. Bycatch data was collected during two scientific observer programs conducted in the late 1990s and in the late 2000s. Over these two time periods, we compared the temporal trends in bycatch species composition, the probability of occurrence of functional groups per fishing set, the spatio-temporal species richness and the potential impact on several species listed in the red list of the International Union for Conservation of Nature (IUCN). The analyses were performed separately on the two main fishing modes of the fleet, i.e. sets on free-swimming school sets and on fish aggregating devices (FADs). Owing data quality constraints, we did not estimate bycatch rates. Ours results showed that the species composition of sharks caught on FADs decreased over time. The total species richness was higher for FAD sets than for free-swimming school sets (87 vs. 61 species respectively), such difference is common between fishing modes worldwide. For the species catalogued as threatened by the IUCN, in free-swimming schools, 25.5 % of the species caught during first period increased to 30.4 % during second period, while for FAD-fishing the increase was from 28.8 % during first period to 34.9 % in second period. Ours findings suggest that tropical tuna purse-seine fisheries should include ecosystem-based governance of bycatch. Effective tuna management will require a combination of technological improvements for mitigating incidental catch of vulnerable species, best use of byproduct species, regulations in fishing practices and in spatial distribution of fishing effort, and international agreements that, together, can monitor and manage bycatch, reducing the negative fishing effects on the epipelagic ecosystem biodiversity.     

REACTIONS OF CAPTIVE HARBOR PORPOISES (PHOCOENA PHOCOENA) TO PINGER-LIKE SOUNDS

Pingers on gill nets can reduce bycatch of harbor porpoises. If harbor porpoises habituate to pingers, the effect may be reduced or lost. Two captive harbor porpoises were exposed to three sound types. All sounds were in the frequency band from 100 kHz to 140 kHz, 200 ms long, and presented once per 4 s. The source level was 153 dB re 1 μPa RMS at 1 m. Each session consisted of a 10‐min presound, a 5‐min sound, and a 10‐min postsound period. Behavior was recorded on video and on dataloggers placed on the dorsal fin of one animal. The loggers recorded heart rate, swimming speed, dive duration, and depth. The animals responded most strongly to the initial presentations of a sound. Surface time decreased, the heart rate dropped below the normal bradycardia, and echolocation activity decreased. The reactions of both animals diminished rapidly in the following sessions. Should the waning of responsiveness apply to wild animals, porpoises may adapt to the sounds but still avoid nets, or the bycatch may increase after some time. The success of long‐term use of pingers may then depend on the variety of sounds and rates of exposure.     

Impact factors of purse seine net and dip net fisheries on a chub mackerel population

There are two major kinds of fisheries for the chub mackerel in Japan. The purse seine net fishery exploits young and adult fish during the foraging season, while the dip net fishery exploits fish before and during the spawning season. To compare the damage to the chub mackerel stock caused by purse seine net and dip net fisheries, we introduced impact factors of the two kinds of fisheries on the two kinds of fisheries and estimated number of eggs spawned in 1982. We defined the impact factor as the ratio of the average reproductive value of individuals caught by each fishery to the reproductive value at maturity. The number of individuals caught by the purse seine net fishery was 66 times larger than the number caught by the dip net fishery, while the impact factor of the former was 84% of that of the latter. Thus, the total damage caused by the purse seine net fishery was much higher than the damage caused by the dip net fishery. We can evaluate the damage caused by mortality factors on endangered species using this method.     

Evaluation of the effectiveness of light streamer tori-lines and characteristics of bait attacks by seabirds in the western North Pacific

To improve the effectiveness of tori-lines it is necessary to evaluate the ability of tori-lines to mitigate seabird bycatch and determine what kind of seabird species gather during line settings, attack the bait and are incidentally caught. We conducted two experiments in the western North Pacific and examined the effectiveness for seabird mitigation of light streamer tori-lines which have no long streamers but many light (short) streamers and are mainly used in the North Pacific area. Firstly, the effectiveness of two different types of tori-line (light streamer (1 m) and long streamer (up to 7 m) tori-line) and of two different colors (yellow and red) of light streamers for seabird bycatch avoidance was evaluated using 567 sets based on data from 20 offshore surface commercial longliners. No significant difference in the bycatch number between the different tori-line types and streamer colors was found. Secondly, we investigated the characteristics of the seabird bycatch in the North Pacific and the effectiveness of three different types of streamers (light, hybrid and modified light types) by detailed observations of seabird attacks using a chartered longline vessel. Although the appearance rate of albatrosses and shearwaters were 40.9% and 27.7%, Laysan albatross was the main seabird species that followed the vessel but shearwaters seldom followed the vessel and did not aggregate during line setting. In all attacks on bait observed during line settings, 81% and 7% were by albatrosses and shearwaters, respectively. In the number of primary attacks by Laysan albatrosses which attacked most aggressively of all seabirds, there were no significant differences among the tori-line types. No individuals of shearwater were caught. The results of both experiments indicated that light streamer tori-lines were as effective as tori-lines with long streamers for mitigating seabird bycatch in the North Pacific.     

Factors influencing dolphin depredation in coastal fisheries of the northern Aegean Sea: Implications on defining mitigation measures

Dolphin interactions with coastal fisheries are of major concern, reportedly leading to gear damage, which increases the cost of coastal fishing globally and in the Mediterranean Sea. The aim of this study was to determine the effect that gear, target species, mesh size, depth, soaking duration, fishing area, and season have on net depredation frequency and to offer insights on possible mitigation solutions. From November 2013 to February 2016 we monitored 107 active coastal fishers in 22 ports of the northern Aegean Sea coastline, identified the main target species of the fishery and recorded the damages on gill nets and trammel nets caused by dolphins, mainly the common bottlenose dolphin (Tursiops truncatus). Quasi-binomial generalized linear models were used to determine the relationship between the examined factors and depredation frequency. The analysis revealed that the gears mostly depredated were gill nets and trammel nets with small mesh sizes, mainly targeting surmullet (Mullus surmuletus), red mullet (Mullus barbatus), common sole (Solea solea), European hake (Merluccius merluccius), and caramote prawn (Melicertus kerathurus). The probability of depredation was also significantly dependent on the fishing area.     

FEEDING PREFERENCES OF THE MONKEY MIA DOLPHINS: RESULTS FROM A SIMULTANEOUS CHOICE PROTOCOL

The semiwild beach-feeding bottlenose dolphins ( Tursiops aduncus ) of Monkey Mia, Western Australia, provide an unparalleled opportunity to examine prey preference of this species. In a series of binary-choice feeding experiments, we took advantage of the animals' willingness to be fed by hand, to explore their preferences for fish species, size, and state (freshly caught or previously frozen). At the end of each beach visit, each dolphin was provided with a pair of fish but allowed to eat only the first one chosen. The dolphins appeared indifferent among the three species of fish offered to them (yellowtail trumpeter, Amniataba caudovittatus ; striped trumpeter, Pelates sexlineatus ; and western butterfish, Pentapodus vitta ), which were of similar body form and matched for mass. Overall, the dolphins showed a slight preference for the larger of two yellowtail trumpeter offered, suggesting the capability for rational choice when there was a basis for it (most likely energy in this case), although there was considerable individual variation. The dolphins did not distinguish between freshly caught and previously frozen yellowtail. The methodology we describe can be used to generate data of potential value for understanding food and habitat selection of wild dolphins, and for modifying management practices for semiwild dolphins at Monkey Mia and elsewhere.     

插网网目尺寸及采样时间对潮沟游泳动物采样的影响

在长江河口九段沙盐沼湿地的一条潮沟中,我们比较了两种不同网目尺寸（4mm和8mm）的插网（fyke net）及日夜潮对游泳动物群落采样效率的影响。共捕获鱼类16种5476尾、虾2种4982只。采用方差分析、柯尔莫诺夫-斯米尔诺夫非参数检验法和无度量多维标定分析对两种网目插网的捕获效率,样品的体长分布,群落结构及日夜潮间的差异进行了分析。结果表明,网目尺寸对样品中游泳动物的物种数和鱼类的多度没有影响,但是小网目的插网对虾类有较高的捕获率。两种网目尺寸的插网均在夜潮中捕获较多的鱼类个体,但虾类在日潮捕获较多。在日潮中,网目尺寸对捕获物中五种优势游泳动物的体长分布无显著影响。在夜间,小网目的插网对斑尾复缎虎和脊尾白虾的较大个体具有较高的捕获率,但对较大个体鲅的捕获率不如大网目的插网。样品中游泳动物的群落组成在日夜潮间存在明显差异,大网目捕获物的样本间差异比小网目小。