Average Fork Length Research Articles

Spawning aggregations of checkered snapper (Lutjanus decussatus) and blackspot snapper (L. fulviflamma): seasonality, lunar-phase periodicity and spatial distribution within spawning ground.

Snappers (family Lutjanidae) are important fisheries target species and some species are known to form spawning aggregations at particular spawning grounds. The present study investigated the ecological characteristics of fish aggregations of two snapper species (checkered snapper Lutjanus decussatus and blackspot snapper L. fulviflamma) that form at a particular site. Specifically, the aims were to clarify (1) seasonality and lunar-phase periodicity of fish aggregation formation, (2) fine-scale spatial distribution of fish density (spatial variations of fish density at intervals of several-tens meters) within the aggregation site, (3) size and age frequency distributions of fishes in the aggregation site, (4) gonad development, (5) to compare fish abundance between inside and outside the aggregation site, and (6) to verify that fish aggregations of the two snapper species were spawning aggregation. Underwater observations using a 600m×5m transect revealed that greater fish abundance of Lutjanus decussatus was found monthly between May and October, and clear positive peaks in the fish abundance were found only around the last-quarter moon. This lunar-related periodicity in the increase of fish abundance was confirmed by a time-series analysis (correlogram). Within the aggregation site, L. decussatus showed a relatively uniform distribution. In contrast, greater fish abundance of L. fulviflamma was found monthly between April and October, and clear positive peaks in the fish abundance were found around the last-quarter moon (April, May, June and October) or new moon (July, August and September). This lunar-related periodicity was also confirmed by correlogram. Lutjanus fulviflamma showed a relatively clumped distribution within the aggregation site. Most females of the two species in the aggregation site had hydrated eggs, indicating that the two species form aggregations for reproduction. The two species, although occurring simultaneously, are considered to form aggregations of conspecifics only. For L. decussatus, average fork length and age of males and females were 229.2 mm and 243.9 mm and 9.4 years and 8.1 years, respectively. For L. fulviflamma, average fork length and age of males and females were 233.9 mm and 246.9 mm and 6.8 years and 8.1 years, respectively. Fish abundance inside the aggregation site was 266.8-fold and 141557.1-fold greater than those outside the aggregation site for L. decussatus and L. fulviflamma, respectively. These results showed that (1) fish aggregation formation of the two snapper species was predictably repeated in particular months and lunar-phase, (2) it was predictably found at the particular site, (3) the fish abundance in the aggregation site markedly exceeded the fish abundance outside the aggregation site, and (4) the two species form aggregations for reproduction. Therefore, it is suggested that the fish aggregations for the two species can be regarded as spawning aggregations.

Catch per unit effort, condition factor and length-weight relationship of albacore tuna (Thunnus alalunga), yellowfin tuna (Thunnus albacares) and bigeye tuna (Thunnus obesus) in the longline tuna fishery in the Eastern Pacific Ocean

Highly migratory tuna species play an important economic role and ecosystem function worldwide. They are mainly caught in tropical and subtropical areas of the Pacific, Atlantic and Indian oceans. Data collected by the Chinese longline fishery in the high seas of the Eastern Pacific Ocean from 2014 to 2015 were analysed to estimate the catch per unit effort (CPUE), length and weight frequency, length-weight relationship, relative condition factor and Fulton’s condition factor for albacore tuna (Thunnus alalunga), yellowfin tuna (Thunnus albacares) and bigeye tuna (Thunnus obesus). The results showed that this fishing technique was highly selective for these three species. Albacore tuna represented the major portion of the catches at 76.17%. Yellowfin and bigeye tuna represented 8.24 and 11.68% of the total of specimens, respectively. The remaining 3.9% were bycatch such as Katsuwonus pelamis, Acanthocybium solandri, Ruvettus pretiosus, Xiphias gladius, Lampris guttatus, Carcharodon carcharias and Scomberomorus guttatus. The average fork length for albacore tuna was 90-100 cm; yellowfin tuna, 100-130 cm and bigeye tuna, 125-165 cm. The average weight for albacore tuna was 15-20 kg; yellowfin tuna, 20-50 kg and bigeye tuna, 35-55 kg. The CPUE (based on fish per one thousand hooks) for albacore, yellowfin tuna and bigeye tuna ranged from 1.6 to 9.82, 1.07 to 2.66 and 1.06 to 3.45, respectively. The parameters of the length-weight relationship showed a negative allometric growth regression of 2.7135 for albacore tuna, 2.3275 for yellowfin tuna and 2.4047 for bigeye tuna. Nevertheless, the albacore and yellowfin tuna females were characterised by positive allometry (b>3). The analyses also showed that the relative condition factors (Krel) of the three fish species were greater than one, implying that they were in good physiological condition, good water quality and healthy organisms. Keywords: China, Fishing effort, Fish per hook, Tuna

Distribution of skipjack tuna (<italic>Katsuwonus pelamis</italic>) associated with a light falling-net in the South China Sea

We investigated the distribution and the in-situ target strength (TS, dB) of the skipjack tuna <italic>Katsuwonus pelamis</italic> associated with light falling-nets in the South China Sea using the Simrad EY60 scientific echosounder. The volume backscattering strength (<italic>S</italic>v, dB), TS, and mean number of fish per sampled volume (<italic>N</italic>_V) were studied. The average fork length of skipjack tuna in the S13, S14, and A12 stations were (362.20±35.73) mm, (357.66± 36.61) mm, and (366.70±36.43) mm, respectively. There was no significant difference in the average fork length among the three stations (<italic>P</italic>&gt;0.05). Within the depth range of 10–50 m, the mean <italic>S</italic>_V change pattern of the three stations at different time phases was similar. Before the fishing lights were turned on (18:00–19:00), the <italic>K. pelamis</italic> was mainly distributed at a water depth of 40–50 m; after the lights turned on, the <italic>K. pelamis</italic> was gradually attracted and floated, and thus the depth corresponding to the peak of the <italic>S</italic>_V distribution curve became shallower. With the increase of lighting time (20:00–21:00), the <italic>K. pelamis</italic> was stably distributed at a depth range of 10–30 m. In the depth range of 10–50 m, the number of individual signals at the three stations in different time phases was also similar to the mean depth change pattern. Before the fishing lights were turned on (18:00–19:00), the signals were mainly distributed at a depth of 35 m, and few signals were detected. After the lights were turned on, <italic>K. pelamis</italic> were gradually attracted and floated, resulting in a shallower mean depth of the signals, and the number of signals increased significantly. There were no <italic>N</italic>_V limit values at the three stations in this study, and all cells can be used for the in-situ TS calculation. The mean in-situ TS was (–51.84±3.84) dB at the S13 station, (–49.87±3.72) dB at the S14 station, and (–49.68±2.96) dB at the A12 station. The in-situ TS of <italic>K. pelamis</italic> at the three stations were non-normally distributed (<italic>P</italic>&lt;0.05). These results help us better understand the fish behavior and acoustic characteristics under the conditions of light trapping and also set up a technical foundation for future acoustic evaluation.

Impacts of salmon lice on mortality, marine migration distance and premature return in sea trout

Brown trout Salmo trutta (L.) is a facultative anadromous species, where a portion of individuals in populations with access to the sea perform migrations to use the richer feeding resources. We investigated the effect of salmon lice Lepeophtheirus salmonis (Krøyer 1837) infestation on the survival and behaviour of wild trout post-smolts (average fork length = 180 mm) during their marine migration. Comparisons of the marine migratory behaviour were made between an artificially infested group (n = 74) and a control group (n = 71) in an area with low natural lice infestation pressure. Artificial infestation was estimated to cause 100% prevalence and a mean intensity of 65 lice fish-1 (mean relative intensity of 2.4 lice g-1 fish). Survival analysis showed limited statistical power but revealed lice-induced mortality, with an estimated hazard ratio of 2.73 (95% CI = 1.04-7.13) compared to the control group, when data from a previous pilot study were included. Surviving individuals in the infested group additionally responded by residing closer to fresh water while at sea, and by prematurely returning to fresh water. On average, infested fish returned to fresh water after only 18 d at sea, while control fish spent on average 100 d at sea. The residency in the inner part of the fjord and the premature return to fresh water represent an adaptive behavioural response to survive the infestation, at the probable cost of reduced growth opportunities and compromised future fitness.

Body condition and reproductive status of chum salmon during homing migration in Otsuchi Bay, Japan, after the 2011 Great East Japan Earthquake and Tsunami

To understand how the earthquake and tsunami on March 11 2011 affected homing chum salmon Oncorhynchus keta in Otsuchi Bay, Japan, we monitored the body condition and reproductive status at the mouth of the bay in October, November, December, and January from 2012 to 2016. The average fork length in 2014 was larger than that in 2012 and 2015, due to the high proportion of 5- and 6-year-old salmon and the low proportion of 3- and 4-year-old salmon, possibly because of the decrease in the salmon fry released by the hatchery program after the disaster. Plasma estradiol-17β (E2) concentrations in females were high in October and November and declined in December and January, whereas plasma 11-ketotestosterone concentrations in males were consistently high throughout the sampling period. Plasma 17α,20β-dihydroxy-pregnen-3-one (17α,20β-P) increased in both sexes in December and/or January. These changes were consistently observed from 2012 to 2016; however, the rise in 17α,20β-P and decline in E2 levels in female salmon in December were conspicuous in 2013 and 2014, reflecting changes in age composition. These results suggest that the earthquake and tsunami temporarily affected the age composition and the physiological condition of chum salmon returning to Otsuchi Bay.

Comparing some biological characteristics of two sturgeons species, Persian sturgeon (Acipenser persicus Borodin, 1897) and Russian sturgeon (A. gueldenstaedtii Brandt & Ratzeburg, 1833) in the Caspian Sea

The objective of this study was to compare biological parameters such as length, weight, age, caviar production indices, caviar/weight, growth, condition factor and sex ratios of Persian sturgeon (Acipenser persicus Borodin, 1897) and Russian sturgeon (A. gueldenstaedti Brandt & Ratzeburg, 1833) in the Caspian Sea during 1990-2014. The results showed that a variety of differences between this two species. All these characteristics (except condition factor) of Persian sturgeon were greater than Russian sturgeon. In the long period, the average (±SD) fork length ranged from 129.3 (±11.87) to 140.9 (±15.99) cm and 145.7 (±17.61) to 157.4 (±19.31) cm for the Persian sturgeon. The caviar harvest for the Russian sturgeon ranged from 3.86 (±1.05) to 5.02 (±1.82) kg with a caviar/weight ratio were ranged from 16.9 (±4.12) to 20.1% (±5.12), while comparatively for the Persian sturgeon was greater and ranged from 4.84 (±1.62) and 7.04 (±2.58) kg with a caviar/weight ratio of 16.2 (±3.99) to 21.1 (±5.20) %. The age of both species ranged between 6 to 40 years but the modal age of Russian sturgeon was less than Persian sturgeon. The male:female sex ratio of Russian and Persian sturgeons were 0.23:1 and 0.57:1, respective. The sex ratio of Russian sturgeon was significantly different from sex ration of Persian sturgeon (P <0.001). The condition factor of Russian sturgeon were 0.92 (±0.16) and 0.74 (±0.13) % for Russian sturgeon and Persian sturgeon. Also, results of the MANOVA revealed significant differences in community structure of two species (P < 0.001). Therefore, different conservation and management activity need for these two valuable sturgeons in the Caspian Sea.

Investigations on the age, growth and mortality parameters of Kawakawa, Euthynnus affinis (Cantor, 1849) from the North west coast of India

Kawakawa, Euthynnus affinis contributes to the tune of 35,466 tonnes forming 1% to the total marine fish landings of India. Investigations on growth and mortality were of this species carried out based on the length frequency data during 2008-2012. The length-weight relationship for the pooled samples were derived for intercept a=0.0286, slope b=2.857 and coefficient of determination r 2 =0.917. The values obtained for growth parameters of L∞ was 67.86 cm, for growth coefficient (K) 0.70 and for t o -0.26y -1 . The natural, total and fishing mortalities recorded as 0.86, 1.48 and 0.62 y -1 ,respectively. The exploitation ratio (F/Z) was observed as 0.42. The M/K ratio was estimated at 1.23. The average fork length of 46 cm and weight of 2024 g were estimated in the samples collected. The length at the end of 1 st year to 5 th year was observed to be 33, 52, 64, 70 and 75 cm, respectively. The fishing mortality derived in this study is more than the optimum and limit value indicated the sign of overexploitation.

Estuarine and marine diets of out-migrating Chinook Salmon smolts in relation to local zooplankton populations, including harmful blooms

Changes in food availability during the early marine phase of wild Chinook Salmon (O. tshawytscha) are being investigated as a cause of their recent declines in the Salish Sea. The marine survival of hatchery smolts, in particular, has been poor. This part of the Salish Sea Marine Survival Project examined the diet of young out-migrating Chinook Salmon for four consecutive years in the Cowichan River estuary and in Cowichan Bay, British Columbia, Canada. Local zooplankton communities were monitored during the final year of the study in the Cowichan River estuary, Cowichan Bay, and eastward to the Salish Sea to better understand the bottom-up processes that may be affecting Chinook Salmon survival. Rearing environment affected body size, diet, and distribution in the study area. Clipped smolts (hatchery-reared) were larger than the unclipped smolts (primarily naturally-reared), ate larger prey, spent very little time in the estuary, and disappeared from the bay earlier, likely due to emigration or mortality. Their larger body size may be a disadvantage for hatchery smolts if it necessitates their leaving the estuary prematurely to meet energy needs; the onset of piscivory began at a forklength of approximately 74 mm, which was less than the average forklength of the clipped fish in this study. The primary zooplankton bloom occurred during the last week of April/first week of May 2013, whereas the main release of hatchery-reared Chinook Salmon smolts occurs each year in mid-May—this timing mismatch may reduce their survival. Gut fullness was correlated with zooplankton biomass; however, both the clipped and unclipped smolts were not observed in the bay until the bloom of harmful Noctiluca was finished—20 days after the maximum recorded zooplankton abundance. Jellyfish medusa flourished in nearshore areas, becoming less prevalent towards the deeper waters of the Salish Sea. The sizable presence of Noctiluca and jellyfish in the zooplankton blooms may be repelling young salmon from a critical early marine food source and reducing their survival.

SIZE AND GROWTH VARIATION AT MATURITY OF SIX NEMIPTERUS SPECIES IN THE SOUTH CHINA SEA

This study was aimed to observe the variation in size and growth change at maturity stage of both sexes for six Nemipterus species in the southern part of the Gulf of Thailand. Sample were collected using bottom trawl net was operated on board of “MV PRAMONG 9” research vessel during April -June, 2015. Male maturity stage-III of all fish species displayed largest average fork length 19.0±1.8, 11.1±2.6, 11.3±2.0, 19.3±4.4, 19.6±0.8 and 17.5±0.2, respectively. Similarly, female maturity stage-II was showed largest range of fork length 16.8±1.4, 9.8±0.3, 16.6±1.1, 16.3±1.3 and 16.5±0.9, respectively except N. mesoprion. Male fish was found larger in size than female for all species. Growth rate was higher at early stage of life for male fish and higher in adult for female fish. All species namely S. taeniopterus, N. mesoprion, N. furcosus, N. tambuloides and N. hexodon showed negative allometry according to growth value “b” observation except in N. nematophorus (positive allometry) in different maturity stages. Therefore, this study results can be used to help the fishery managers which can be used for maintain sustainable condition of Nemipteridae fish resources in the Gulf of Thailand and leading to a greater boost in the economy of Thailand.

Nearshore Distribution of Pacific Sand Lance (Ammodytes personatus) in the Inland Waters of Washington State

Abstract Pacific Sand Lance (Ammodytes personatus) are energy-rich schooling fish that are thought to be important drivers of marine food webs in Alaska (USA) and British Columbia (Canada). Despite a number of studies characterizing their distribution and habitat use in Alaska and British Columbia, surprisingly little is known about population attributes in the Salish Sea. We compiled and analyzed 15,192 records collected from 1630 sites, primarily by beach seine or tow net in nearshore shallow areas between 1970 and 2009, to determine Sand Lance spatial and seasonal distribution in the inland waters of Washington State. Sand Lance were present along 78% of the shoreline that was sampled and were captured during every month of the year. The maximum number captured in individual nets increased between May and August. Fork length ranged from 1.7 to 19.0 cm and average fork length did not vary by month. The shortest minimum fork lengths were documented during April through July, likely representing annual re...

Effect of Replacement of Maize Gluten with Rice Bran (5:0 and 1:4) Feed Supplement on Fish Growth in a Composite Culture

This experiment was conducted to evaluate comparative effect of replacement of maize gluten with rice bran feed supplement on fish growth in composite culture. Two earthen ponds, each measuring 30m x 16m x 1.5m (length x width x depth) were stocked with 100 Labeo rohita, 50 Cirrihina mrigla and 25 Ctenophayrngon idella. Pond P1 was provided maize gluten and rice bran with a ratio 5:0 whilst pond P2 was provided maize gluten and rice bran with a ratio 1:4. Average body weight gain, fork length and total length were affected significantly by replacing maize gluten with rice bran. Results indicated that it is better to supplement maize gluten (30% CP): rice bran 1:4 for more yield as compared to maize gluten (30% CP) alone.

Antibiotic susceptibilities of bacteria isolated within the oral flora of Florida blacktip sharks: guidance for empiric antibiotic therapy.

Sharks possess a variety of pathogenic bacteria in their oral cavity that may potentially be transferred into humans during a bite. The aim of the presented study focused on the identification of the bacteria present in the mouths of live blacktip sharks, Carcharhinus limbatus, and the extent that these bacteria possess multi-drug resistance. Swabs were taken from the oral cavity of nineteen live blacktip sharks, which were subsequently released. The average fork length was 146 cm (±11), suggesting the blacktip sharks were mature adults at least 8 years old. All swabs underwent standard microbiological work-up with identification of organisms and reporting of antibiotic susceptibilities using an automated microbiology system. The oral samples revealed an average of 2.72 (±1.4) bacterial isolates per shark. Gram-negative bacteria, making up 61% of all bacterial isolates, were significantly (p<0.001) more common than gram-positive bacteria (39%). The most common organisms were Vibrio spp. (28%), various coagulase-negative Staphylococcus spp. (16%), and Pasteurella spp. (12%). The overall resistance rate was 12% for all antibiotics tested with nearly 43% of bacteria resistant to at least one antibiotic. Multi-drug resistance was seen in 4% of bacteria. No association between shark gender or fork length with bacterial density or antibiotic resistance was observed. Antibiotics with the highest overall susceptibility rates included fluoroquinolones, 3rd generation cephalosporins and sulfamethoxazole/trimethoprim. Recommended empiric antimicrobial therapy for adult blacktip shark bites should encompass either a fluoroquinolone or combination of a 3rd generation cephalosporin plus doxycycline.

Impact of Costa Rican longline fishery on its bycatch of sharks, stingrays, bony fish and olive ridley turtles (Lepidochelys olivacea)

We used data collected by an observer program to assess the impact of the Costa Rican longline fishery on numbers, capture locations, seasonality and body sizes of silky sharks (Carcharhinus falciformis), pelagic thresher sharks (Alopias pelagicus), olive ridley turtles (Lepidochelys olivacea) and other bycatch species in the Central American Pacific. The longline fishery caught a large number of mahi-mahi (Coryphaena sp.) and silky sharks, but also caught a large number of olive ridley turtles and pelagic stingrays (Pteroplatytrygon violacea). We estimated that longline fisheries caught 699,600 olive ridleys, including 92,300 adult females, from 1999 to 2010. These captures were associated with a decline of nesting populations at nearby arribada beaches. There were statistically significant size decreases from 1999 to 2010 in mature olive ridley turtles and from 2003 to 2010 in silky sharks. Average fork length of silky sharks in 2010 was 97.3cm, which was far below observed fork length at maturity, 144cm. Pelagic thresher sharks were small and fluctuated in size over the study period. Capture of large numbers of juvenile blacktip sharks (Carcharhinus limbatus) indicated a nursery area near the Osa Peninsula. Geospatial analysis indicated shifts in mahi-mahi abundance on a temporal scale but fishing efforts did not shift with the shift in mahi-mahi abundance. Yellowfin tuna (Thunnus albacares), Indo-Pacific blue marlin (Makaira mazara) and Indo-Pacific sailfish (Istiophorus platypterus) catches varied seasonally and were most abundant out to sea and south of Panama. Marine protected areas and/or time area closures are needed to reduce the impact of the Costa Rican longline fishery on sea turtles and sharks.

Long-term changes in fecundity of the Kutum, Rutilus frisii kutum Kamensky, 1901, in the Caspian Sea (Osteichthyes: Cyprinidae)

Changes in length, weight and fecundity of mature females of the Kutum (Rutilus frisii kutum) were compared for the periods 1948–1950, 1974 and 2007 in Iranian waters of the Caspian Sea. The average fork length decreased from 54.1 over 44.7 to 43.9 cm and the average weight from 2181 over 1295 to 1210 g. However, the average condition factor has remained fairly constant and varied between 1.35 and 1.38. The potential fecundity of the Kutum for the three periods also decreased from 106,800 over 74,600 to 64,400 eggs. Size and fecundity of the Caspian Kutum has therefore sharply declined during the last six decades. The reduction of fecundity is apparently the consequence of the shift towards smaller fish size.

Body size trends along vertical and thermal gradients of chum salmon in the Bering Sea during summer

Relationships between the vertical distribution and thermal habitat, and body size of chum salmon Oncorhynchus keta were studied in the Bering Sea in summer using trawl surveys at various depths. Chum salmon abundance decreased with increasing depth, but the patterns of decrease differed between size groups. The abundance of small salmon fell rapidly with depth, whereas that of large salmon decreased gradually to 40 m depth, and abruptly below that. The average fork length of chum salmon collected from each trawl correlated positively with trawl net depth and negatively with water temperature. Since the optimal temperature for growth decreases with body size in this species, the observed body size-related vertical habitat use by chum salmon may indicate size-dependent thermal preferences.

Juvenile Coho Salmon Leaping Ability and Behavior in an Experimental Culvert Test Bed

AbstractAs part of a research program aimed at identifying the culvert configurations and associated hydraulic conditions that foster the successful upstream movement of juvenile salmon, we investigated the ability of hatchery‐raised juvenile coho salmon Oncorhynchus kisutch to leap into an experimental culvert under varying hydraulic conditions. Five outfall drops ranging from 0 to 32 cm were tested to represent differing degrees of culvert outfall drop. Trials were run at a culvert discharge of 0.028 m3/s and a tailwater pool depth of 30 cm. The median success rate was highest (85%) for the 0‐cm drop, followed by 34% at 12 cm, 20% at 20 cm, 2% at 26 cm, and 0% at 32 cm. When overcoming the 0‐cm (streaming flow) and 12‐cm drops, fish predominantly used swimming behavior. For the outfall drops of 20 and 26 cm, leaping behavior predominated. In a typical leaping event, fish initiated the leap near the floor of the tailwater tank and used burst swimming to propel their bodies from near the standing wave (produced by the fall of water exiting the culvert) into the culvert entrance. Both high‐ and low‐trajectory leaps were observed; some fish attained a height up to 5.2 times their body length. The average fork length of fish that were successful at culvert entry was 103 mm (SD, 1.4), compared with 101 mm (1.3) for those that remained in the tailwater pool. Within the size range of the test population, 60‐135 mm (mean, 103 mm), fish size did not affect ability to enter the culvert under the test conditions. These results indicate that juvenile coho salmon are capable of overcoming some degree of culvert perch to move upstream if tailwater pool water depth and pool size are sufficient and hydraulic passage conditions inside the culvert are favorable.

Changes in the Population Ecology of Hatchery and Wild Coho Salmon in the Strait of Georgia

AbstractAn analysis of the results of a 10‐year study of the population ecology of juvenile hatchery and wild coho salmon Oncorhynchus kisutch in the Strait of Georgia produced new information about the interannual and interseasonal fluctuations in abundance and marine survival. A decline in the percentage of hatchery coho salmon was related to declines in hatchery fish abundance and marine survival; wild coho salmon abundance was more stable. The declining marine survival of hatchery coho salmon appeared to be related to a fixed average date of release from hatcheries and a possibility of earlier prey production. The relatively stable abundance of wild coho salmon may relate to a natural trend toward earlier ocean entry dates. Oscillations in hatchery coho salmon percentage and abundance were related to oscillations in abundance of juvenile pink salmon O. gorbuscha. The impact of oscillating density affected marine survival of hatchery coho salmon more than that of wild coho salmon. Marine survival and abundance of hatchery and wild coho salmon in July were positively related to average fork length, indicating that growth within the first few months after ocean entry affected marine survival. However, absolute size was not important, as wild coho salmon were consistently smaller than hatchery coho salmon. Wild coho salmon responded to conditions in the marine ecosystem differently than hatchery coho salmon, as relationships among growth, survival, and abundance were apparent for wild coho salmon earlier in the year than for hatchery fish. The length increase between July and September was inversely related to marine survival, suggesting that fish that were larger in July grew less and survived better because they were storing more lipids than smaller coho salmon. The study indicated that a more experimental management strategy is needed for both hatchery and wild coho salmon.

Covariation between the average lengths of mature coho (Oncorhynchus kisutch) and Chinook salmon (O. tshawytscha) and the ocean environment

AbstractWe used the average fork length of age‐3 returning coho (Oncorhynchus kisutch) and age‐3 ocean‐type and age‐4 stream‐type Chinook (Oncorhynchus tshawytscha) salmon along the northeast Pacific coast to assess the covariability between established oceanic environmental indices and growth. These indices included the Multivariate El Niño‐Southern Oscillation Index (MEI), Pacific Decadal Oscillation (PDO), Northern Oscillation Index, and Aleutian Low Pressure Index. Washington, Oregon, and California (WOC) salmon sizes were negatively correlated with the MEI values indicating that ultimate fish size was affected negatively by El Niño‐like events. Further, we show that the growth trajectory of WOC salmon was set following the first ocean winter. Returning ocean‐type British Columbia‐Puget Sound Chinook salmon average fork length was positively correlated with the MEI values during the summer and autumn of return year, which was possibly a result of a shallower mixed layer and improved food‐web productivity of subarctic Pacific waters. Size variation of coho salmon stocks south of Alaska was synchronous and negatively correlated with warm conditions (positive PDO) and weak North Pacific high pressure during ocean residence.

Electroshocking and PIT Tagging of Juvenile Atlantic Salmon: Are There Interactive Effects on Growth and Survival?

AbstractElectroshocking and tagging of fish with passive integrated transponder (PIT) tags are two commonly used methods for conducting mark–recapture studies in freshwater environments and are frequently used in combination. We conducted an experiment to test for the effects of electroshocking, tagging, and a combination of electroshocking plus tagging on the growth and survival of Atlantic salmon Salmo salar parr. We used five treatments that included the presence or absence of PIT tags and electroshocking at 300 or 500 V plus a control group. Fish were measured, weighed, and electroshocked on four occasions separated by approximately 2‐month intervals. The average (±1 SD) fork length was 62.1 ± 1.9 mm and the average weight was 2.5 ± 0.3 g at the start of the experiment; at the end of the experiment, length averaged 120.5 ± 11.6 mm and weight averaged 20.9 ± 6.1 g. We did not detect any significant effects of electroshocking on growth or survival over the course of the experiment. However, there was evidence that tagging negatively influenced survival over the first interval after initial tagging and that survival was positively correlated with fish size. In addition, tagged fish seemed to suffer a minor depression in growth over the first interval, although differences in size among tagged and untagged fish were nonsignificant throughout the course of the experiment. We suggest that the size at tagging may have a greater effect on survival and growth of small (&lt;80;eqmm) Atlantic salmon parr than the amount of exposure to electroshocking.

Density‐dependent growth of young‐of‐the‐year Atlantic salmonSalmo salarin Catamaran Brook, New Brunswick

SummaryWhile density‐dependent mortality and emigration have been widely reported in stream salmonid populations, density‐dependent growth is less frequently detected. A recent study suggests that density‐dependent growth in stream salmonids occurs at low densities, whereas density‐dependent mortality and emigration occur at high densities.To test the hypothesis that density‐dependent growth occurs primarily at low rather than at high densities, we examined the relationship between average fork length and population density of young‐of‐the‐year (YOY) Atlantic salmon at the end of the growing season using a 10‐year data set collected on Catamaran Brook, New Brunswick. We tested whether (1) average body size decreases with increasing density; (2) the effect of density on average body size is greatest at low densities; (3) growth rate will decrease most rapidly at low effective densities [Σ(fork length)2]; (4) density‐dependent growth is weaker over space than over time; and (5) the strength of density‐dependent growth increases with the size of the habitat unit (i.e. spatial scale) when compared within years, but not between years.There was a strong negative relationship between the average body size and population density of YOY Atlantic salmon in the autumn, which was best described by a negative power curve. Similarly, a negative power curve provided the best fit to the relationship between average body size and effective density. Most of the variation in average body size was explained by YOY density, with year, location and the density of 1+ and 2+ salmon accounting for a minor proportion of the variation.The strength of density‐dependent growth did not differ significantly between comparisons over space vs. time. Consistent with the last prediction, the strength of density‐dependent growth increased with increasing spatial scale in the within‐year, but not in the between‐year comparisons.The effect of density on growth was strongest at low population densities, too low to expect interference competition. Stream salmonid populations may be regulated by two mechanisms: density‐dependent growth via exploitative competition at low densities, perhaps mediated by predator‐induced reductions in drift rate, and density‐dependent mortality and emigration via interference competition at high densities.