Stock enhancement in a commercial mullet,Mugil cephalus L., fishery in Hawaii

Abstract This study showed that cultured striped mullet, Mugil cephalus L., released as juveniles can make a significant contribution to landings in an island commercial fishery. Following pilot hatchery releases from 1990 to 1993, striped mullet fisheries in Kaneohe Bay, Hawaii, USA, were sampled to recover cultured fish from the bay-wide catch. Direct sampling of 181 fishing trips resulted in recovery of 211 cultured striped mullet. By autumn 1994, cultured fish comprised 13.0% (2.8%) of the commercial mullet catch in Kaneohe Bay, and the percentage was increasing logarithmically. This study corroborated predictions from previous studies of juveniles about effects of release strategies on survival of cultured mullet. Following summer releases, recapture rates were strongly affected by fish size-at-release, with a critical release size of 60 mm total length (the smallest size released that was subsequently detected in the fishery). Over 30 000 juveniles stocked in 1990 (but not in a nursery habitat preferred by striped mullet) apparently suffered complete mortality.     

Sea-ranching of brown trout, Salmo trutta L.

Abstract  In total, 8211 1-year-old and 14839 2-year-old hatchery-reared brown trout, Salmo trutta L., from 11 stocks were released at the mouth of the River Imsa, southwestern Norway. The recapture rates and total estimated yield were higher for 2- than 1-year-old trout, although recapture rates varied between years of release and stocks. The recapture rate increased with mean individual weight at time of release. Total estimated yield from the individual groups of 1+ trout ranged from 2 to 20 kg per 1000 trout released and for 2+ trout between 11 and 250 kg per 1000 fish released. In all cases, yields were lower than the economic break-even yield. Most fish were recaptured the year of release (89.2% of 2+ and 76.2% of 1+ trout). Almost 31% of the recaptures were caught at sea and 69% in fresh water; 95.8% of the latter were taken in the River Imsa trap.     

Significance of Fish Size-At-Release on Enhancement of Striped Mullet Fisheries in Hawaii

A tag-release-recapture study was conducted to evaluate size-at-release impacts upon recruitment of cultured, juvenile striped mullet, Mugil cepahlus released in inshore habitats of Oahu, Hawaii, USA. In June and July 1990, 85,848 juvenile mullet were graded into five size groups (ranging from 45 to 120 mm in length), identified with binary-coded wire tags, and released into two estuaries (2×5 factorial design). Of the tagged fish, 42,822 were released into Kaneohe Bay on the east (windward) coast of Oahu; 43,026 were released into Maunalua Bay on Oahu's dryer south shore. The fish were released into both bays simultaneously. Releases were blocked in time across 5 release lots. To evaluate growth and survival rates of released mullet, both bay systems were sampled monthly with cast nets over a ten-month period after release. Overall, 733 tagged M. cephalus were recaptured, 277 from Kaneohe Bay and 456 from Maunalua Bay. Overall proportions of tagged fish in samples declined from 33.4% (±25.2%) of the total M. cephalus catch at week 5 to 1.88% (±0.95%) by week 23. From week 23 on, tagged fish averaged 2.09% (±0.23%) of the striped mullet in monthly samples. Within 9 wk after releases, recapture frequencies were clearly skewed in favor of fish that were larger at the time of release. Fish smaller than 70 mm when released were rare or absent in collections within 18 wk after release. This confirms results of a smaller-scale pilot study in Maunalua Bay and shows that fish size-at-release can have a major impact on the success of hatchery releases in marine habitats. Pilot studies to identify minimum fish size-at-release should be conducted at all sites targeted for full-scale marine hatchery releases.     

Influence of gear switching on recapture of Atlantic salmon (Salmo salar) in catch‐and‐release fisheries

Anglers that release Atlantic salmon (Salmo salar) in recreational fisheries do so with the intention that the fish will survive and contribute to succeeding generations. In some instances, salmon that are released may be recaptured, but mechanisms associated with recapture are unclear. To test whether gear avoidance influences recapture rates, we analysed data from tagging programmes in major Norwegian Atlantic salmon fishing rivers to determine how frequently salmon were recaptured by different gear than that by which they were initially captured (i.e. gear switch). Among 339 salmon captured, externally tagged and released in 2012 and 2013, 46 (14%) were recaptured; 70% of these recaptured salmon exhibited gear switch. To test whether this gear switch percentage could be expected in the absence of gear avoidance, a simulation was conducted, which accounted for variation in catch probability among rivers and across time with different gear types based on comprehensive catch data. Each simulation step provided a simulated rate of gear switch under the null hypothesis of no gear avoidance. A distribution was generated, which described the probability that we would observe 70% gear switch. The simulated results indicated that this rate of gear switch was highly unlikely (P = 0.003) if recapture gear is assumed to be independent of initial capture gear, suggesting that salmon avoided familiar gear types. Changes to behaviour after release, including learned hook avoidance, may explain our observation of gear avoidance by recaptured salmon.     

Vulnerability-size effects of electric fishing on population estimate, size distribution and mean weight of a sea trout, Salmo trutta L., stock

A dynamic mark-recapture electric fishing study on sea trout, Salmo trutta L., was carried out from July 1989 to January 1990. There was a significant difference in the recapture probability ( P = R / M ) between small (24–39 cm) and large (40–84 cm) sea trout with P- values of 0.31 and 0.62, respectively (χ² = 16.52, P < 0.001). The vulnerability-size relationship resulted in a slight overestimation of population size (2.5%) using the Petersen method by adding the two size classes together in the computations. Separate computations for the two size classes had no significant effect upon the estimate of the seasonal length distributions but a significant effect on the estimates of total length distribution ( P < 0.001) and the mean weight of the mature stock ( P < 0.001). The present data emphasises that size-selectivity should be taken into account in electric fishing studies on adult sea trout.     

Residency of adult Atlantic cod (Gadus morhua) in the western Gulf of Maine

A mark and recapture study of cod in the western Gulf of Maine was conducted to study the seasonal movements of fish, particularly as they related to areas closed to commercial fishing. A total of 27,772 cod were tagged, and 1334 (4.8%) were recaptured with sufficiently detailed recapture location and date to be included in the study. Results indicated that the group is resident to the area and sedentary. Although there were a small percentage of fish (2.5%) that traveled long distances (>100 km), most were recaptured near their release location. There was no linear relationship between fish length and linear distances traveled, and linear distance traveled was only weakly related to days-at-large. For all groups of cod tagged and released in particular areas and months, mean distances traveled were small (<65 km), rates of travel were slow (<0.2 km/day), and rates of group dispersion were <50 km²/day. There were no recognizable spatial or temporal patterns in the mean angles of travel for groups released in various month/area combinations, and the angular deviations associated with the mean angles were quite large. Although there seems to be little pattern in the movement of cod in our study area, temporal and spatial changes in abundance indicate that movements are occurring.

The general pattern was a concentration of large cod into one small, inshore area (Area 133) in both the spring and winter, and dispersion from this area in the ensuing months. Monthly percentages of ripe cod in Area 133 provide evidence for two spawning groups; a winter group that spawns from November through January, and a spring group that spawns from April through July. Thus it is likely that the observed spring and winter concentrations of fish in Area 133 were associated with spawning. Fish in the spring group were the largest encountered in the study. The study also provided some evidence of natal homing, i.e. a return to the same spawning grounds year after year, for the spring spawning group. Although there is some exchange of fish between most of the closed areas, the timing of the closures appears to protect the largest aggregations of cod.     

Dispersal and growth rate of O-group salmon (Salmo salar L.) from point-stocking together with some information from scatter-stocking

Abstract– Experiments on the dispersal of O-group salmon from a 'point-stocking' were made in 1988, 1989, 1990 and 1991 in Bollihope Burn, Co. Durham. Experiments on 'scatter-stocking' were made in 1992 and 1993, but the 1992 experiment was aborted for technical reasons. In each year the fish were stocked as fry in spring and their distribution in September was ascertained by electrofishing. Some fish from point-stocking dispersed up to 50 m upstream or 500 m downstream of the stocking point, but the majority remained close to the stocking point. This gave rise to considerable spatial variation in September population density and fish weight, which could be modelled by semi-logarithmic curves. Survival from point-stocking was 19% and 14% in 1988 and 1989, respectively. Approximately 20 to 25% of the September survivors from point-stocking were found upstream of the release point. Scatter-stocking gave relatively little variation in population density or fish weight in September, and estimated survival was 27%.     

The enhancement of abalone stocks: lessons from Japanese case studies

The dramatic declines in abalone Haliotis spp. fishery production have been documented all over the world. Release of hatchery‐reared juveniles into natural habitats has been considered as one measure to sustain and/or augment the current fishery production of abalone, as well as to restore collapsed abalone stocks. However, attempts at abalone release programmes have only been undertaken at experimental scales, except for Japan, where large‐scale stock enhancement programmes for abalone have been undertaken since late 1960s. To evaluate the potential of stock enhancement for abalone, we analysed the release surveys of 13 case studies in Japan in terms of the overall recapture rate (number of recaptures through a lifetime/number of juveniles released), yield per release (YPR, yields from released individuals), the economic efficiency of releases (ratio of income from recaptured abalone to release cost) for each release year, and the contribution of hatchery releases to total catches for each fishing year. The average estimates for overall recapture rates (0.014–0.238) and YPR (3.1–60.3 g/individual) varied between locations and release years. The economic efficiency was estimated at 0.4–6.2. The released abalone contributed 6.9–83.5% to total catches. Hatchery releases could augment total production at some locations, but the success of release programmes would be limited by the carrying capacity at release areas, because density‐dependent mortality occurred following releases in some cases. Throughout Japan, the annual catch of abalone has continuously declined from ～6500 t in 1970 to ～2000 t in the mid‐1990s, despite the increase in the number of hatchery releases. Based on the estimates for YPR, the magnitude of the abalone releases on a national scale has not been sufficiently large to sustain the total production of Japanese abalone, which has primarily fluctuated according to the abundances of wild populations. Our results suggest that releases should be targeted at local populations in regions where stock enhancement is predicted to have the greatest chance of success, and the magnitude of releases should be considered carefully and determined for each region by taking the local carrying capacity into account. We also address the future prospects of abalone stock enhancement.     

The risk of individual fish being captured multiple times in a catch and release fishery

The proportion of angled Atlantic salmon Salmo salar L. being caught and released has increased. If individuals are repeatedly captured, this may have fish welfare consequences. Of 995 Atlantic salmon tagged during catch and release in eight Norwegian rivers, 10% were captured twice, while 3% were captured three times within the same fishing season. The probability that released salmon were captured again decreased with decreasing time left of the fishing season, decreased for larger‐sized fish and varied among rivers/years. Increased exploitation rates within the river, indicating an increased fishing pressure, strongly increased the probability that fish would be recaptured. However, the proportion of salmon caught a second time was much lower than the total exploitation rates in the same rivers (which was on average 46%). For fish tagged in the sea, the likelihood of being angled decreased with time since entering the river, which may explain why the recapture rates of caught and released fish were lower than the total exploitation rates.     

Investigating the catch returns and growth rate of wels catfish, Silurus glanis, using mark–recapture

Abstract In January 2004, 46 wels catfish, Silurus glanis L., between 51 and 135 cm total length were tagged and released into a 0.4 ha recreational, catch and release, lake fishery in the UK, and their recapture by anglers monitored throughout the year. Of the 46 tagged fish, 16 were recaptured by anglers during 170 capture events. Some individual fish were captured up to 26 times. Catfish <75 cm appeared to be the least susceptible to capture and fish >100 cm most susceptible. Frequency of captures increased with temperatures >10 °C and peaked between June and August. Selected recapture weight data were used to produce a mass specific growth equation and revealed specific growth rate was a decreasing function of body mass over the size range of the recaptured fish. Their growth was slower than fish from elsewhere in their distribution range.     

大亚湾黑鲷标志放流及回捕率调查

为评价大亚湾海域黑鲷(Acanthopagrusschlegelii)增殖放流效果,使用塑料椭圆标志牌(plasticovaltags,POTs),开展了黑鲷幼鱼标志保持率与生长实验。结果显示,背鳍鳍棘基部第4～6鳍棘下方5mm左右的背部肌肉为最适标志位置, 90 d后标志保持率为81.76%。POTs标志黑鲷幼鱼45 d内生长与对照组无显著性差异(P>0.05),而90 d后标志组生长显著缓于对照组(P<0.05)。并于2014—2016年每年1次在大亚湾开展黑鲷幼鱼标志放流试验。采用有奖回收方式进行标志鱼回捕,测量体长、体重,收集回捕日期、回捕地点、回捕方式等信息,整理分析相关数据。3年共放流标志黑鲷幼鱼60115尾,共2758尾回捕标志鱼被定置网、流刺网及垂钓捕获(总回捕率4.59%);大规格放流苗种回捕率高于小规格放流苗种;垂钓回捕鱼数量占总回捕数量的比例为62.08%。通过对反馈信息的分析,认为放流后的标志鱼最初主要沿湾内和湾外两个方向呈近岸辐射状扩散,最远扩散距离约70 km。放流后1～2个月标志黑鲷生长较慢,随后相对加快,放流5～7个月后,黑鲷幼鱼体长、体重分别增长59.51%～127.20%和322.75%～989.83%。结论认为,POT是黑鲷幼鱼体外标志的适宜选择;在研究海域,放流后的标志黑鲷更易于被垂钓方式捕获;丰富的食物和可供躲避敌害的空间是影响其扩散、生长的因素。     

Recapture of pond- and hatchery-reared brown trout, Salmo trutta L., released in small streams

Abstract. Two groups of 0+ brown trout, Salmo trutta L., one pond-reared and one hatchery-reared (fish length 32-80mm), were released in eight small streams in three different areas of Norway between 1984 and 1987. Hatchery and pond fish were reared at different sites, but releases were made both near the rearing site and in the home area of the other group. A total of 2550 fish were recaptured by electrofishing the year after stocking. We found great variations in the recapture rates of pond and hatchery fish in one stream between years, and between streams in different areas the same year. These results indicate that the rearing method is not essential to the recapture rate. Both pond and hatchery fish generally had higher recapture rates in streams near their rearing site than in the distant areas. Thus factors associated with transportation seem to influence the survival of stocked fish. The results also indicate that size at stocking may be an important factor for the recapture rate.     

Dispersion of stocked brown trout, Salmo trutta L., and landlocked salmon, Salmo salar L., from stocking sites in Lake Oulujärvi, Finland

Movement and recaptures of two hatchery-reared brown trout, Salmo trutta L., stocks and landlocked salmon, Salmo salar L., released at different sites in regulated Lake Oulujärvi, were studied in relation to release site. Five groups of fish from each stock were released in approximately equal numbers. Most of the fish released in June and July were recaptured within 3 months, whereas the majority of the fish released in early winter (October and November) were caught the following spring, about 7–9 months after stocking. The release site had a significant effect on recapture rate. The results showed that fishing restrictions targeted mainly at gill net fishing are needed to preserve the stocked fish from overfishing. Significantly fewer recaptures were observed from the landlocked salmon stocking compared with brown trout. The recaptures from the landlocked salmon stocking indicated more active movement and less clumping compared with the two brown trout stocks.     

Effects of smolt size and timing of migration on recovery rate of wild masu salmon <Emphasis Type="Italic">Oncorhynchus masou</Emphasis>

Little is known about the survival rate of wild masu salmon Oncorhynchus masou. To examine the effects of smolt length and migration timing on the recovery rate of wild masu salmon, we reanalyzed past tagging and recovery data (1993–1994). The tagging study was conducted in the Shokanbetsu River, northern Japan; 863 wild masu salmon smolts were captured, tagged, and released in a downstream site, and a total of 19 fish were recovered in coastal fisheries and in the natal river the following year. The data were analyzed by a logistic regression analysis with recapture as a response variable and tagging date and smolt length as explanatory variables; the tagging date had a significant effect on the recapture rate, whereas the effect of smolt size was not significant. Despite the small number of recaptures, this study indicates that migration timing is a factor affecting the marine survival of wild masu salmon smolts, although this conclusion has been repeatedly documented for other species of Pacific salmon Oncorhynchus spp.     

Assessment of recapture rates after hatchery release of Chinese shrimp Fenneropenaeus chinensis in Jiaozhou Bay and Bohai Bay in 2012 using pedigree tracing based on SSR markers

We calculated the recapture rates for Chinese shrimp Fenneropenaeus chinensis following hatchery release in Jiaozhou Bay and Bohai Bay in 2012 based on parentage identification using simple sequence repeat (SSR) markers. The results and process were as follows: In total, 3 × 10⁵ postlarval Chinese shrimp (inner marker), comprising six full-sib families, were released into Jiaozhou Bay with a hatchery release of approximately 9 × 10⁷ same-sized stock in the spring. Eight shrimp (inner marker) were identified from 2,507 recapture catches in the autumn, with information about eight SSR loci available by using Cervus 3.0. Similarly, another six full-sib families, comprising 2.04 × 10⁵ postlarvae, were released into Bohai Bay with a hatchery release of approximately 1.6 × 10⁸ same-sized Chinese shrimp of postlarval stock, and four shrimp were identified from 3,232 recapture catches in the autumn. Furthermore, we calculated the number of released stock in the recapture catches, i.e., 2,400 and 3,137 in Jiaozhou Bay and Bohai Bay, respectively. Combined with statistics for Chinese shrimp resources during the autumn fishing season, we calculated that the recapture rates for Jiaozhou Bay and Bohai Bay were 2.70 and 2.59 %, respectively, being slightly lower but more precise compared with results obtained using traditional methods (2.81 and 2.67 %).     

放流三疣梭子蟹月间回捕率及繁殖贡献率研究

2015年6月,将约500万只人工繁育的三疣梭子蟹C2期稚蟹放流到辽宁盘锦沿岸海域.当年7月28日—10月3日在盘锦沿岸以地笼网回捕1671只三疣梭子蟹样本,剪其螯足,剥离肌肉,提取DNA,利用微卫星DNA分子标记进行亲子鉴定,开展个体识别.试验结果显示,120只为当年放流蟹,放流后苗种短期月间放流蟹占当月回捕蟹群体的...     

Effects of release timing on migration behaviour and survival of hatchery‐reared Atlantic salmon smolts in a regulated river

In this study, 221 two‐year‐old hatchery‐reared salmon, Salmo salar, smolts were tagged with radio transmitters over a period of three consecutive years and released in the river in groups of 20–21 fish in various dates between late April and early June. Tagged smolts were tracked during their downstream migration in the lower 36‐km stretch of the regulated River Oulujoki, with the focus on the effects of release date, water temperature and river flow on migration behaviour and survival. The results indicate that release timing and river temperature have profound effects on the initiation of migration, swimming speed and survival of released S. salar smolts. Smolts released early in the spring in cold waters ceased migration after brief downstream movement and were vulnerable to predation, whereas the migration speed and survival rates increased markedly for smolts released later in the spring.     

青岛市古镇口湾增殖放流日本对虾的生长特性

对青岛市古镇口湾放流日本对虾Penaeus japonicus的生长特性进行了研究。结果表明,雄虾生长较快,而雌虾能达到更大的个体,雌虾体重生长拐点在91d前后,雄虾为77d,合理开捕日期为9月中旬,可适当把放流日期提至6月初。9月中旬前放流日本对虾生长期主要集中分布于5m等深线以内泥沙底质海区。     

魁蚶底播增殖的试验研究

魁对是一种适应性强、生态效率高的大型经济贝类。种苗投放后成活率可达99%,1年后的回捕率在50%以上;在满足魁蚶习性要求的一般条件下,选择敌害少,海底稳定性好的海区是增殖成败的关键。蟹类(如梭子蟹、日本虫寻)对种苗危害极大,并可能导致“全军覆没”的后果;种苗放流没有严格的时间要求.壳长2.0～2.5cm 可作为放流种苗的标准规格。放流1～1.5年后可达5～7cm 商品规格,增殖效果显著,适用于生产性魁蚶资源增殖放流。     

High marine survival rates of sea‐ranched Atlantic salmon smolts (Salmo salar) that had previously matured as male parr

Abstract The growth and recapture rates of Atlantic salmon, Salmo salar L., smolts that had previously matured as parr were compared with those of immature siblings in a sea‐ranching experiment in western Norway. The smolts were the offspring of three river populations. They were individually tagged, transferred to cages in a small bay where estuarine salinity gradients had been established and released on four dates from mid‐May to early June after either 3 or 7 days of acclimatisation. The previously mature male parr (PMMP) were smaller than their siblings before release, but performed much better during their time in the sea. As grilse, they reached sizes comparable with the formerly immature fish, and their recapture rate was more than four times higher (8.6 vs 2.1%). This difference decreased somewhat during the following years because 0.85% of the immature fish and only 0.1% of PMMP were recaptured as multi‐sea‐winter salmon. The highly successful marine performance of the PMMP demonstrated that this life history strategy may be more flexible than previously believed.