Takashi Matsuishi

Effects of sampling errors on abundance estimates from virtual population analysis for walleye pollock in northern waters of Sea of Japan

Effects of sampling errors on abundance estimates from virtual population analysis (VPA) were quantified with the bootstrap method for stock of walleye pollock in the the Sea of Japan. In the bootstrap method, individual fish measurements were resampled. A total of 1000 bootstrap samples were produced for each year from 1991 to 2001. The coefficients of variation (CV) of catch at age in 2001 ranged 6.1–33.1%. The CV of an abundance estimate in 2001 ranged 9.0–35.7%. Abundance estimates of the oldest age and the latest year, which had larger CVs than the other estimates, were sensitive to sampling errors. Effects of sampling errors became smaller when the catch at age had been accumulated over a few years. Although VPA includes various types of errors, only the sampling errors have room for improvement in reality. Quantifying the effect of sampling error on VPA estimates is essential for sound and efficient stock management, and is emphasized in this study.

Brown adipose tissue in cetacean blubber.

Brown adipose tissue (BAT) plays an important role in thermoregulation in species living in cold environments, given heat can be generated from its chemical energy reserves. Here we investigate the existence of BAT in blubber in four species of delphinoid cetacean, the Pacific white-sided and bottlenose dolphins, Lagenorhynchus obliquidens and Tursiops truncates, and Dall’s and harbour porpoises, Phocoenoides dalli and Phocoena phocoena. Histology revealed adipocytes with small unilocular fat droplets and a large eosinophilic cytoplasm intermingled with connective tissue in the innermost layers of blubber. Chemistry revealed a brown adipocyte-specific mitochondrial protein, uncoupling protein 1 (UCP1), within these same adipocytes, but not those distributed elsewhere throughout the blubber. Western blot analysis of extracts from the inner blubber layer confirmed that the immunohistochemical positive reaction was specific to UCP1 and that this adipose tissue was BAT. To better understand the distribution of BAT throughout the entire cetacean body, cadavers were subjected to computed tomography (CT) scanning. Resulting imagery, coupled with histological corroboration of fine tissue structure, revealed adipocytes intermingled with connective tissue in the lowest layer of blubber were distributed within a thin, highly dense layer that extended the length of the body, with the exception of the rostrum, fin and fluke regions. As such, we describe BAT effectively enveloping the cetacean body. Our results suggest that delphinoid blubber could serve a role additional to those frequently attributed to it: simple insulation blanket, energy storage, hydrodynamic streamlining or contributor to positive buoyancy. We believe delphinoid BAT might also function like an electric blanket, enabling animals to frequent waters cooler than blubber as an insulator alone might otherwise allow an animal to withstand, or allow animals to maintain body temperature in cool waters during sustained periods of physical inactivity.

Increase of inbreeding by stocking on wild population assessed by using individual-based life history model

The genetic impact of stocking on natural populations was assessed by using individual-based life history models. Models were constructed that included density-dependent mortality at the early life stage, natural mortality, fishing mortality, and the number of released fish. These variables were varied by using random numbers. The focus was on the genetic impact of the number of released fish, the number of parent fish producing seedlings that were released, the sex ratio of the parent fish, fishing mortality, and the methods to select the parents of the seedlings. When brood stock size in the hatchery was five males and five females, the coefficient of inbreeding was about 27-fold as high as that in the case of 50 males and 50 females at the 50th generation. The coefficient increased about fivefold at the 50th generation, when the sex ratio of the parents changed from 50 males and 50 females to 10 males and 90 females. When parents were taken from wild populations at random, extreme fishing mortality reduced genetic diversity.

Seasonal distribution of harbour porpoise (Phocoena phocoena) in Japanese waters inferred from stranding and bycatch records

Abstract. Little is known about the biology of harbour porpoises (Phocoena phocoena) around Japanese waters. This study estimates the seasonal distribution of harbour porpoises in Japan using 240 stranding and bycatch records from 1966 to August 2009 deposited at the Institute of Cetacean Research, Tokyo, the Stranding Network Hokkaido, Hokkaido, and records summarized in a previous study. Over 70% of all the records were bycatch from use of three types fishing gear: large set-nets, other type set-nets, and gill nets. Most of the bycatch records were derived from Usujiri, Hokkaido, where a regular monitoring survey on harbour porpoises caught incidentally by large set-nets has been conducted since the 1980s. These records showed that harbour porpoises migrate to the coast of Honshu (mainland of Japan) in the winter, and move north in the summer. Their latitudinal range coincided with the sea surface temperature (SST) range between 6 and 17°C. Additionally, the stranding and bycatch records which were found only from April to June in Funka Bay, Hokkaido suggested that Funka Bay is used only for a few months in spring. Overall, the present study clarifies the finer seasonal distribution of harbour porpoise around Japan, and its strong dependence on SST.

Application of Cohort Analysis to Large Terrestrial Mammal Harvest Data

Abstract. Cohort analysis (also known as virtual population analysis) is a method of population reconstruction from age-specific harvest data. Because cohort analysis requires data over a whole life span to reconstruct a population for a single year, this method is impracticable for longer-lived animals. Three models are routinely combined by fisheries scientists to make cohort analysis more cost effective and to provide real-time estimates of population size; these models may be applied to large terrestrial mammal harvest data. Each model has unique assumptions about hunting mortality rates or age distributions, and the reliability of estimates depends on meeting these assumptions. In this study, we first tested previously used assumptions for these models through an analysis of long-term moose (Alces alces) harvest data, followed by an examination of the robustness of estimates for each moose age class. We developed practical ways to achieve more realistic assumptions for two of three models and showed that meeting these assumptions was more important in estimations of large terrestrial mammal population parameters than for fish population parameters. Therefore, we recommend compliance with assumptions of the three models for more reliable population estimates of large terrestrial mammals.

Weight-based population analysis: an estimation method

Generally, the individual weight of large fish is measured at landing, and thus, their weight composition is easily obtained. In this paper, we develop a method of population analysis using weight composition of fish, called weight-based population analysis, or WPA. WPA needs data of catch-at-weight, weight composition, weight from the growth and natural mortality M. We apply the method to the walleye pollack fishery in Funka Bay to evaluate its validity. The results show that the population size estimated from WPA reflects the features of population dynamics, and the estimated parameters reflect this walleye pollack fishery. Further, we compare the results of WPA with those of virtual population analysis (VPA) using catch-at-age data. The trend of population dynamics estimated using WPA was comparable to the results of VPA, suggesting that WPA can estimate population size as well as VPA.

Stable isotope ratios of carbon, nitrogen and oxygen in killer whales (Orcinus orca) stranded on the coast of Hokkaido, Japan.

We analyzed δ(13)C, δ(15)N and δ(18)O in the muscle and liver from killer whales stranded on the coast of Japan. The δ(15)N values in the muscle samples from calves were apparently higher than those in their lactating mothers, suggesting that nursing may result in the higher δ(15)N values in the muscle samples of calves. The δ(15)N value in the muscle samples of male and female whales, except for the calves, were positively correlated with the δ(13)C values and body length, suggesting that the increases in δ(15)N were due to the growth of the whales and increase in their trophic level. In contrast, the δ(18)O values in the muscle samples of female whales except for the calves were negatively correlated with the δ(13)C and δ(15)N values. The δ(18)O may be lower in whales occupying higher trophic positions (δ(15)N), although it might also be affected by geographic and climatic conditions.

Fish Diversity and Abundance of Lake Tanganyika: Comparison between Protected Area (Mahale Mountains National Park) and Unprotected Areas

High biodiversity is the most remarkable characteristic of Lake Tanganyika including vertebrates, invertebrates, and plants. A few protected areas have been created along the lake to protect its biodiversity. However, limited studies have been carried out to ascertain their effectiveness. The current study aimed at assessing and comparing fish diversity and abundance of Lake Tanganyika in a protected area (Mahale Mountains National Park (MMNP)) and unprotected areas surrounding it. The data were collected in the near shore zone at 5 m and 10 m depths using stationary visual census (SVC) technique. The protected area recorded higher fish richness and abundance than unprotected areas (). It was concluded that the protected area is effective in conserving the fish diversity and abundance of the lake. However, more studies should be carried out regularly to explore the efficacy of the protected area in conservation of aquatic biodiversity and abundance.

Accumulation of hydroxylated polychlorinated biphenyls (OH-PCBs) and implications for PCBs metabolic capacities in three porpoise species

The present study investigated polychlorinated biphenyls (PCBs) and hydroxylated metabolites of PCBs (OH-PCBs) in blood from three porpoise species: finless porpoises (Neophocaena phocaenoides), harbor porpoises (Phocoena phocoena), and Dalls porpoises (Phocoenoides dalli). The porpoises were found stranded or were bycaught along the Japanese coast. Concentrations of OH-PCB were the highest in Dalls porpoises (58pgg(-1) wet wt), second highest in finless porpoises (20pgg(-1) wet wt), and lowest in harbor porpoises (8.3pgg(-1) wet wt). The concentrations in Dalls porpoises were significantly higher than the concentrations in finless porpoises and harbor porpoises (p<0.05 and p<0.01, respectively). There was a positive correlation between PCB and OH-PCB concentrations (r=0.67, p<0.001), suggesting the possible concentration-dependent induction of CYP enzymes. The three porpoise species may have exceptionally low metabolic capacities compared with other marine and terrestrial mammals, because low OH-PCB/PCB concentration ratios were found, which were 0.0016 for Dalls porpoises, 0.0013 for harbor porpoises, and 0.00058 for finless porpoises. Distinct differences in the OH-PCB congener patterns were observed for the three species, even though they are taxonomically closely related.

Weight-based yield per recruitment and spawning-biomass per recruitment analyses of Pacific cod Gadus macrocephalus off the Pacific coast of southern Hokkaido, Japan

The present study assessed the stock state of Pacific cod Gadus macrocephalus caught off the coast of southern Hokkaido, Japan. Weight-based yield per recruitment (YPR) and spawning-biomass per recruitment (SPR) analyses were used for this assessment. The current fishing mortality (average from 1998 to 2000) was 0.65 and weight at first capture was 0.5 kg bodyweight. Under these fishing pressures, the YPR of Pacific cod in southern Hokkaido was 1.06 kg/recruitment and percentage of SPR (%SPR) was 6.9%. The %SPR was lower than the critical limit at 20%SPR. The main reason that values of both YPR and %SPR were not optimum, would be that the weight at first capture was too small. Raising the weight at first capture was thought to be a better strategy from the biological viewpoint, and reducing fishing mortality to 0.3 would be the next alternative strategy from the fisheries management viewpoint.