Habitat differentiation between sei (Balaenoptera borealis) and Bryde's whales (B. brydei) in the western North Pacific

Two closely related baleen whale species, sei and Bryde's whales, in the western North Pacific were studied to identify differences in habitat use. Data were obtained from May to August 2004 and 2005. This study examined the relationship between oceanographic features derived from satellite data and the distribution of sei and Bryde's whales using basic statistics. We investigated oceanographic features including sea surface temperature (SST), sea surface chlorophyll a (Chl‐a), sea surface height anomalies (SSHAs), and depth of the habitat. These two whale species used habitats with different SST, Chl‐a, and SSHA ranges. The 0.25 mg m^?3 Chl‐a contour (similar to the definition of the Transition Zone Chlorophyll Front) was a good indicator that separated the habitats of sei and Bryde's whales. Then generalized linear models were used to model the probabilities that the whale species would be present in a habitat and to estimate their habitat distribution throughout the study area as a function of environmental variables. The potential habitats of the two species were clearly divided, and the boundary moved north with seasonal progression. The habitat partitioning results indicated that SST contributed to the patterns of habitat‐use and might reflect differences in prey species between the two whales. This study showed that the habitats of the sei and Bryde's whales were clearly divided and their potential habitat‐use changed seasonally.     

Dual effects of reversed winter–spring temperatures on year‐to‐year variation in the recruitment of chub mackerel (Scomber japonicus)

To clarify the effects of temperature on the recruitment of chub mackerel (Scomber japonicus) in the North Pacific, we investigated the influence of winter surface temperature (WST) on spawners at the time of maturity around the spawning grounds and the influence of ambient spring temperature on larvae using estimated temperature (ET) obtained from particle tracking experiments. We found a significant positive correlation between ET approximately 10 days following hatching and the recruitment per spawning stock biomass (RPS) after 2000. The closer (more meandering) the Kuroshio Current (KC) axis was in relation to the spawning ground, the higher (lower) the spring surface temperature and the higher (lower) RPS was in the spawning ground. In contrast, WST inside KC near the maturity/spawning ground was significantly negatively correlated with RPS. A significant negative correlation between the temperatures in winter and spring was detected in the area after 2000, when the conditions of the Pacific decadal oscillation index and the stability of the Kuroshio Extension were synchronous, indicating that KC shifted northward during this time. The reversed temperature pattern was consistent with the winter–spring movement of KC axis in the offshore direction and was correlated with the winter–spring difference in the intensity of the Aleutian low. These results suggest that the annual variation in chub mackerel recruitment after 2000 was strongly affected by the combined effects of ambient temperature because of the reversal of conditions that occurred between winter and spring around the maturity/spawning ground, which was related to the KC path.     

Structure of the intratesticular duct system for sperm emission in the starspotted smooth-hound Mustelus manazo

We conducted histological observation of male germ cells and reproductive organs of the starspotted smooth-hound Mustelus manazo in Tokyo Bay to reveal any abnormality in male reproductive traits, as part of a study to elucidate the factors causing recent fluctuation in abundance of the population. Spermatogenesis proceeded in spermatocysts from the germinal zone in the ventral part of the testis to the degenerative zone in the dorsal part, where the spermatozoa were conveyed into the ciliated lumina of the attached terminal branches of the intratesticular ducts. The intratesticular ducts were classified from their terminal ends into branch, stem, and collecting tubules. The ducts formed in the germinal zone and grew as the spermatocysts developed. An opening formed through the wall of each of the most mature spermatocysts into a branch tubule; bundles of spermatozoa were evacuated through this opening into the branch and then the stem tubule and subsequently into the collecting tubules in the rete testis and the efferent duct connected to the epididymis. Spermatocysts that were unable to emit sperm because of failure of adhesion to the branch tubules were disorganized in situ, as were their spermatozoa. The collapsed spermatocysts seem to be cleared by hemophagocytosis with lymphocytes and leukocytes, which may have been recruited from the epigonal organ. There were no specific abnormalities in the spermatogenesis or the morphological structure of testes, which suggested that an abnormality of male reproductive traits was not the major cause of the recent fluctuation in the population abundance of this species. Details of the intratesticular duct system for sperm emission to the epididymis are the first findings in elasmobranchs worldwide.     

Effect of feeding rotifers enriched with taurine on the growth and survival of larval amberjack Seriola dumerili

The effect of feeding rotifers enriched with taurine on the growth performance and survival of larval amberjack Seriola dumerili was investigated. Rotifers were enriched with a commercial taurine supplement at four levels (0, 200, 400, and 800 mg/l). The larvae were fed the enriched rotifers in triplicate from 3 days post-hatch for 7 days under static conditions. The average taurine contents of the rotifers were 1.5, 2.7, 4.2, and 7.2 mg/g dry matter, respectively. The growth of the fish fed rotifers enriched with the taurine supplement at 800 mg/l was significantly (P < 0.05) improved compared with that of the fish fed the rotifers without taurine enrichment. The survival rate improved proportionally up to a taurine supplement level of 400 mg/l, but no significant differences in survival were observed among treatments. The fraction of the larvae with inflated swim bladders did not vary significantly between treatments. Taurine content in the whole fish body increased with the taurine level in the rotifers. These results suggest that taurine enrichment of rotifers is an effective method of enhancing the growth of amberjack larvae.     

Application of the Tweedie distribution to zero-catch data in CPUE analysis

We focus on the zero-catch problem of CPUE (catch per unit effort) standardization. Because the traditional CPUE model with a log-normal error structure cannot be applied in this case, three methods have often been utilized as follows:

(1) Ad hoc method adds a small constant value to all response variables.

(2) Catch model with a Poisson or negative-binomial (NB) error structure.

(3) Delta-type two-step method such as the delta-normal model (after estimating the ratio of zero-catch using a logit or probit model, a model such as CPUE log-normal or Catch-Poisson is applied to CPUE without zero-data).

However, there are some statistical problems with each of these methods.In this paper, we carried out the CPUE standardization mainly using the Tweedie distribution model based on the actual by-catch data (silky shark, Carcharhimus falciformis, in the North Pacific Ocean caught by Japanese training vessels) including many observations with zero-catch (>2/3rd) and tuna fishery data as a target (yellowfin tuna, Thunnus albacares, in the Indian Ocean caught by Japanese commercial vessels) where the ratio of zero-catch is not so high (<1/3rd). The Tweedie model is an extension of compound Poisson model derived from the stochastic process where the weight of the counted objects (i.e., number of fish) has a gamma distribution and has an advantage of handling the zero-catch data in a unified way.We also compared four candidate models, the Catch-NB model, ad hoc method, Delta-lognormal model (delta-type two-step method) and Tweedie distribution, through CPUE analyses of actual fishery data in terms of the statistical performance. Square error and Pearson's correlation coefficient were calculated based on the observed CPUE and the corresponding predicted CPUE using the n-fold cross-validation.As a result, the differences in the trend of CPUE between years and model performance between the ad hoc method and Tweedie model were found to be not so large in the example of yellowfin tuna (target species). However, the statistical performance of Tweedie distribution is rather better than Delta-lognormal model, the Catch-NB distribution and ad hoc method in the example of silky shark (by-catch species). Standardized CPUE year trend of ad hoc method was found to be quite different from that of the Tweedie distribution and other two models. Model performance of the Tweedie distribution is good judging from the 5-fold cross-validation using the fishery data if including many zero-catch data such as by-catch species.     

Ability of salmon growth hormone to accelerate somatic growth of juvenil abalone Haliotis discus hannai

ABSTRACT:   The ability of salmon growth hormone (sGH) to accelerate the somatic growth of juvenile abalone Haliotis discus hannai by immersion was examined. After immersion for one hour into a sGH-rich solution at a concentration of 30 mg/L, the sGH immunoreactivity in the body fluid of abalone was maximal after one day, and levels were still detectable at two days. No immunoreactivity was observed in the control group. Following immersion for one hour at one or two-week intervals for 120 weeks into the sGH-rich solution at 30 mg/L, the sGH-immersed abalone exhibited a significant increase in shell length and body weight. On the other hand, abalone immersed into a salmon prolactin (sPRL)-rich solution at 30 mg/L for one hour showed a lower increase in both shell length and body weight than the sGH-immersed abalone. No increases in shell length and body weight were observed in either the bovine serum albumin-immersed abalone or untreated controls. These results provide evidence that sGH can be transported from ambient water into the circulatory system of abalone, and can subsequently improve the somatic growth of juveniles.     

Hemolytic compound 3,7,11,15-tetramethyl-hexadecan-1,19-disulfate found in the invasive European sea squirt Ascidiella aspersa

Fisheries Science - The solitary European sea squirt Ascidiella aspersa was introduced to northern Japan, causing dense coverage of the aquacultured Japanese scallop Mizuhopecten yessoensis. There...     

Relationship between coastal water properties and adult return of chum salmon (Oncorhynchus keta) along the Sanriku coast,Japan

We investigated the relationship between adult (age‐4) return rates for chum salmon (Oncorhynchus keta) originating from the Iwate Prefecture, Japan, and coastal environmental conditions during their early ocean life in coastal residency. We analyzed distributions of water properties via intensive hydrographic observations using a conductivity–temperature–depth profiler. Both the return rates and water properties vary strongly over interannual time scales. We found that the time when the return rate decreased drastically corresponded well to the time when the frequency of warm waters in the coastal residency increased.     

In vivo and in vitro effects of Rhizopus extract on body growth and steroid production in masu salmon, Oncorhynchus masou Brevoort

This study investigated the in vivo and in vitro effects of Rhizopus (filamentous fungus) extract (RU) in masu salmon Oncorhynchus masou Brevoort. Underyearling fish were fed with RU for 16 months. Monthly changes in body growth, gonadal maturation and serum levels of sex steroids were monitored. Gonads were also incubated at 0, 1, 10, 100 and 1000 μg RU mL⁻¹ Leibovitz's L‐15 medium for 18 h. The levels of steroids in serum and cultured medium were measured. It was determined that RU‐fed immature and mature males, when compared with control groups, showed significantly higher body growth during spring, summer and the spawning period. Similarly, immature RU‐fed females showed significantly higher fork length and body weight in autumn, spring and summer. Furthermore, RU‐fed males showed significantly higher levels of serum testosterone (T) and 11‐ketotestosterone (11‐KT) levels in the pre‐spawning season, and 17α, 20β‐dihydroxy‐4‐pregnen‐3‐one (DHP) in the spawning season. In vitro RU incubation of gonads showed a dose‐dependent and significant increase in T, 11‐KT, oestradiol‐17β and DHP release in the medium. It appears that the causes of enhanced body growth and increased steroid production herein observed in salmonids are the physiologically active substances that may be present in the mycelium of the fungus.