Insights from life history traits of Risso's dolphins (Grampus griseus) in Taiwanese waters: Shorter body length characterizes northwest Pacific population

Risso's dolphins (Grampus griseus) are widely distributed throughout temperate to tropical pelagic waters of the world and are one of the most frequently encountered cetaceans in eastern Taiwanese coastal waters. Because their life history is poorly known, the goal of this study was to investigate the relationship between age, body length, and sexual maturity of Risso's dolphins in Taiwanese waters. Ninety‐two carcasses of dead‐stranded or fisheries bycaught dolphins (1994–2008) were measured and dissected (total body length, TBL 125–290 cm); sexual maturity was assessed in 33 dolphins; and age was estimated by counting dentinal growth layer groups in routine histologically prepared tooth sections of 28 dolphins. Sexual dimorphism in TBL was not detected. The onset of sexual maturity occurred at 240–255 cm in females and 253–265 cm in males, which was at about 10 yr of age for both sexes. Our stranding, bycatch, and previous boat survey records suggest that Risso's dolphins occur year‐round and likely have a summer‐fall calving season in Taiwanese waters. The similar life history parameters and calving season in dolphins from Taiwanese and Japanese waters suggest a common population in the northwest Pacific, which has a noticeably shorter body length than in other regions.     

Food partitioning among three sympatric odontocetes (Grampus griseus,Lagenodelphis hosei,and Stenella attenuata)

Food is one of the most important dimensions of resource partitioning for species coexistence. In this study, we investigated the dietary composition and foraging habits of three sympatric odontocetes in order to identify their levels of food niche overlap and ecological separation. Stomach content analysis was performed on samples collected from carcasses confiscated by police or entangled in gill nets from 1994 to 2001, including 27 Risso's dolphins (GG) (Grampus griseus), 27 Fraser's dolphins (LH) (Lagenodelphis hosei), and 45 pantropical spotted dolphins (SA) (Stenella attenuata). GG consumed only cephalopods, with Enoploteuthis chunii accounting for 90.5% of total prey consumed, LH fed on mesopelagic fishes and cephalopods, dominated by hatchetfish, Polyipnus stereope (50.2%), and SA ate both mesopelagic and epipelagic preys, primarily fishes of Myctophum asperum (20.3%) and squids of E. chunii (25.8%). Among the three odontocetes, GG had the narrowest dietary niche width, while SA had the widest width. Both the niche overlap index and the analysis of similarities (ANOSIM) showed significant diet differentiation among these three dolphin species. The depth distribution of their principal prey items further suggests that LH feeds in the deepest waters while SA utilizes prey resources near surface.     

Sex differences in residency patterns of Risso's dolphins (Grampus griseus) in the Azores: Causes and management implications

Knowledge of the residency patterns of marine mammals is an important element for management and conservation strategies. Here we investigate a population of Grampus griseus off Pico Island, Azores. Our data set covers the period 2004–2007, based on at‐sea observations of 1,250 individually identified animals, 303 of known or assumed sex. Using photo identification and GPS locations we calculated mean monthly sighting rates and lagged identification rates to analyze temporal patterns, and estimated kernel density to study the home range. Our results show site fidelity and relatively restricted home ranges, which corroborate the existence of a resident population on the study site. We further document sex differences, including a higher number of males present in the area at any given time but females staying for longer consecutive periods, and male home ranges with significantly less overlap than those of females. These observations are consistent with a mating system based on multimale pods defending areas where females periodically return. We hypothesize that squid distribution is a major factor in structuring these patterns. These findings reinforce the need for a precautionary management approach that would include limiting pressure from commercial activities.     

Annual variability in dentin δ15N and δ13C reveal sex differences in weaning age and feeding habits in Risso's dolphins (Grampus griseus)

Teeth of odontocetes accumulate annual dentinal growth layer groups (GLGs) that record isotope ratios, which reflect the time of their synthesis. Collectively, they provide lifetime records of individual feeding patterns from which life history traits can be inferred. We subsampled the prenatal dentin and postnatal GLGs in Risso's dolphins (Grampus griseus) (n = 65) that stranded or were collected as bycatch in Taiwan (1994–2014) and analyzed them for δ¹⁵N and δ¹³C. Age‐specific δ¹⁵N and δ¹³C values were corrected for effects of calendar year, stranding site, C/N, and sex. δ¹⁵N values were higher in prenatal layers (14.94‰ ± 0.74‰) than in adult female GLGs (12.58‰ ± 0.20‰), suggesting fetal enrichment during gestation. Decreasing δ¹⁵N values in early GLGs suggested changes in dietary protein sources during transition to complete weaning. Weaning age was earlier in males (1.09 yr) than in females (1.81 yr). Significant differences in δ¹⁵N values between weaned males and females suggest potential sexual segregation in feeding habits. δ¹³C values increased from the prenatal to the 4th GLG by ~1.0‰, indicative of a diet shift from ¹³C‐depleted milk to prey items. Our results provide novel insights into the sex‐specific ontogenetic changes in feeding patterns and some life history traits of Risso's dolphins.     

Hector's dolphin diet: The species,sizes and relative importance of prey eaten by Cephalorhynchus hectori,investigated using stomach content analysis

Stomach contents of 63 Hector's dolphins (Cephalorhynchus hectori) were collected between 1984 and 2006 from throughout New Zealand to provide the first quantitative assessment of prey composition. Twenty‐nine taxa were identified. Those most commonly consumed were red cod (Pseudophycis bachus), ahuru (Auchenoceros punctatus), arrow squid (Nototodarus sp.), sprat (Sprattus sp.), sole (Peltorhamphus sp.), and stargazer (Crapatalus sp.). By mass, these six species contributed 77% of total diet. Red cod contributed the most in terms of mass (37%), while ahuru and Hector's lanternfish (Lampanyctodes hectoris) were consumed in large numbers. Prey ranged from <1 cm to >60 cm in total length, but the majority of prey items were <10 cm long, indicating that for some species, juveniles were targeted. Diets of dolphins from South Island east and west coasts were significantly different, due largely to javelinfish (Lepidorhynchus denticulatus) being of greater importance in west coast stomachs, and a greater consumption of demersal prey species in the east. The feeding ecology of Hector's dolphin is broadly similar to that of other Cephalorhynchus species. Hector's dolphin is shown to feed on species from throughout the water column, and differences in diet between populations are thought to reflect prey availability.     

AGE,GROWTH, AND REPRODUCTIVE PATTERNS OF DALL'S PORPOISE (PHOCOENOIDES DALLI) IN THE CENTRAL NORTH PACIFIC OCEAN

Life history parameters were estimated for Dall's porpoise, Phocoenoides dalli, from biological specimens collected in the western Aleutian Islands, during 1981–1987. Of 2,033 males and 3,566 females examined, reproductive data were available for 1,941 males and 1,906 females; ages were determined for 813 males and 1,297 females. Female sexual maturity was based on the presence of one or more corpus on either ovary; 845 were sexually immature and 1,061 were sexually mature. Two estimates of female average age at sexual maturity (ASM) were 3.8 and 4.4 yr; average length at sexual maturity (LSM) was 172 cm. Males were considered sexually mature when evidence of spermatogenesis was detected; 1,136 were sexually immature and 805 were sexually mature. Two estimates of male ASM were 4.5 and 5.0 yr; LSM was 179.7 cm. Physical maturity was assessed for 246 males and 446 females by examining the degree of fusion in thoracic vertebral epiphyses. For both sexes, the average age at physical maturity was 7.2 yr. Average length at physical maturity was 202.6 cm for males and 192.7 cm for females. Average lengths of physically mature males (x?= 198.1 cm, SE = 0.8566) and females (x?= 189.7 cm, SE = 0.4002) were significantly different(P < 0.0001). Early postnatal growth was rapid in both sexes. A secondary growth spurt in both mass and length was characteristic for both sexes; the increase in length preceded the mass increase by 1–2 yr. Average length at birth (LOB) was approximately 100 cm; birth mass averaged 11.3 kg (SE = 0.0772). By the time the umbilicus had healed (<2 mo), the average length and mass had increased to 114.1 cm and 23.8 kg, respectively. Gestation period based on projections using LOB was 12 mo, but this was considered an overestimate. Calving was modal, centered in early July; an annual reproductive interval was indicated. Among the sexually mature females, 120 were pregnant, 55 were pregnant and lactating, 321 were pregnant with colostrum, and 33 were “resting.” By 3 July (95% CI =x? 1 d), 50% of births had occurred, during each of the seven years sampled. The ovulation rate was estimated at 0.914 ovulations per average reproductive year. Enlarged follicles and recent ovulations were observed in postpartum females in late July.     

Age and growth of the bull shark (Carcharhinus leucas) around Reunion Island,South West Indian Ocean

Sharks exhibit varied demographic strategies depending on both the species and the population location, which make them more or less vulnerable to fishing. Accurate evaluation of local age and growth parameters is therefore fundamental for the sustainable management of their stocks. Although demographic parameters have been assessed for bull shark (Carcharhinus leucas) populations in several locations of the world, this information is missing so far around Reunion Island, in the south-west Indian Ocean. To fill this gap of knowledge, age and growth data were gathered from the vertebrae of 140 individuals of C. leucas (77 females and 63 males, mostly adults) fished around the island between 2012 and 2019. After verification of the annual deposition of growth band pairs on these structures using relative marginal increment analysis on 40 individuals, band pairs were counted along the vertebral centrum for each individual. Thanks to this approach, growth was shown to significantly differ between male and female C. leucas around Reunion Island, with respective von Bertalanffy growth model equations of L_t =  and L_t = . Indeed, the females of the species fished in this area were significantly (P < 0.001) larger than local males, with an estimated difference in size of ~16.1 cm at 20 years old. They also apparently reach older ages, with an estimated maximum age of 33.50 years, against 29.75 years only for the males. The estimated size at birth around the island is larger than elsewhere in the world, varying from 92.30 to 100.00 cm depending on the method used. These results confirm that the population of C. leucas around Reunion Island exhibits a K-selected strategy, which makes it highly vulnerable to fishing pressure.     

Physical maturation,life‐history classes and age estimates of free‐ranging western gorillas—insights from Mbeli Bai,Republic of Congo

Physical maturation and life‐history parameters are seen as evolutionary adaptations to different ecological and social conditions. Comparison of life‐history patterns of closely related species living in diverse environments helps to evaluate the validity of these assumptions but empirical data are lacking. The two gorilla species exhibit substantial differences in their environment, which allows investigation into the role of increased frugivory in shaping western gorilla life histories. We present behavioral and morphological data on western gorilla physical maturation and life‐history parameters from a 12.5‐year study at Mbeli Bai, a forest clearing in the Nouabalé‐Ndoki National Park in northern Congo. We assign photographs of known individuals to different life‐history classes and propose new age boundaries for life‐history classes in western gorillas, which can be used and tested at other western gorilla research sites. Our results show that western gorillas are weaned at a later age compared with mountain gorillas and indicate slower physical maturation of immatures. These findings support the risk‐aversion hypothesis for more frugivorous species. However, our methods need to be applied and tested with other gorilla populations. The slow life histories of western gorillas could have major consequences for social structure, mortality patterns and population growth rates that will affect recovery from population crashes of this critically endangered species. We emphasize that long‐term studies can provide crucial demographic and life‐history data that improve our understanding of life‐history evolution and adaptation and help to refine conservation strategies. Am. J. Primatol. 71:106–119, 2009. © 2008 Wiley‐Liss, Inc.     

Life history, aspects of reproductive biology and production of Corophium orientale (Crustacea: Amphipoda) in Monolimni lagoon (Evros Delta, North Aegean Sea)

Monthly samples of Corophium orientale were collected during February 1998–February 1999 in both parts of Monolimni lagoon (0.3 < Sal. < 6 psu, 2 < Temp. < 28.5 °C). Corophium orientaleshowed a semiannual life cycle. In the southern part, breeding occurred from early spring to mid autumn having three peaks, in early spring, early summer and early autumn, and three cohorts were produced, a spring cohort, a summer cohort and an overwintering one. In the shallower innermost northern part of Monolimni lagoon, breeding peaked in mid-spring and, also, in early autumn, and two discrete cohorts, a spring and an overwintering one, were produced. A lack of large individuals, attributed to a temporary size – selective predation by migrating shorebirds, was observed during summer. That lack possibly contributed to the hiatus in reproduction. Photoperiod seemed to be a more important cue than temperature in the initiation of the reproductive cycle, while extremely low salinities (<1 psu) did not deter breeding. Females attained maturity at a smaller size in late spring and, especially, in summer than in early spring at lower temperatures. Brood size was a function of females body size. Females, matured during summer at high temperatures, showed the lowest brood size, body length ratio. Mean brood size was small (12–13 early embryos) and embryo loss during development high (54%), possibly due to a negative effect of low salinities. A 1:1 sex ratio existed in the small body length classes, but females preponderated in the large ones. The spring cohort in the southern part, which developed at moderate temperatures, showed the highest growth rate (40 m day^–1). Secondary production of C. orientalecalculated by Hyness method gave a mean annual density of 4562.5 and 9327.6 ind. m^–2, a mean annual crop (B) of 1.03 and 2.67 g DW m^–2, an annual production (P) of 6.91 and 22.54 g DW m^–2 and a P/B ratio of 6.7 and 8.4 in the northern and southern part of the lagoon, respectively.     

Somatic meiosis in the life history of Bonnemaisonia asparagoides and Bonnemaisonia clavata (Bonnemaisoniales,Rhodophyta) from the Iberian peninsula

Carpospores isolated from Bonnemaisonia asparagoides and Bonnemaisonia clavata (Bonnemaisoniaceae, Rhodophyta) and grown in culture developed into their respective ‘Hymenoclonium’ prostrate phases. In both species, young gametophytes were initiated directly on the prostrate phase from tetrasporangia-like protuberances. Comparison of the relative fluorescence area (rfa) of nuclear DNA over the sequence of life-history stages indicated that the lowest ploidy levels (1–2C) occurred in the gametophytes, whereas the lowest ploidy levels in the prostrate phases were 2–4C. Rfa data demonstrated that meiosis occurred in the tetrasporangia-like protuberances where 1C values were recorded. The present observations establish that B. asparagoides and B. clavata have a heteromorphic diplohaplontic life history, which involves a haploid gametophyte produced directly on a diploid prostate phase after somatic meiosis. We conclude that the life history of these taxa corresponds to the Lemanea-type. This indicates that the life history of several Bonnemaisoniales with a ‘Hymenoclonium’ phase but lacking tetrasporangia requires re-investigation.     

Otolith microstructure and daily age of Anguilla japonica, Temminck & Schlegel elvers from the estuaries of Taiwan with reference to unit stock and larval migration

To test the hypothesis that the Japanese eel, Anguillu japonica , elvers in the eastern and western coasts of Taiwan are recruited from two different spawning grounds and to increase the knowledge of the early life history of the eel, the otolith microstructure and daily age of elvers collected from five estuaries in the coast of Taiwan during December 1989 through February 1990 were examined by scanning electron microscopy. The total length of elvers at arrival in the estuaries was similar among estuaries, averaging c . 56.0 mm and showed a seasonal decrease. The maximum radius of the sagittal otolith of elvers ranged from 124.46 to 181.82μm with a mean of 143.15 ± 12.72 μm. The otolith from centre to edge included an organic-rich primordium (9.20 ± 2.02 μm in diameter), a diffusively calcified core (20.94 ± 1.99 μm), and the daily growth increments; these three layers were probably deposited during the embryonic, yolk sac and feeding period respectively. The growth rate of the otolith was higher at the beginning of early life (0.5−1.0 μm day ⁻¹), lowest at approximately 100-days old (<0.5 μm day⁻¹), and highest 1 month before arrival at the estuary (> 1.0 pm day⁻¹). The mean age for elvers arriving in the estuaries of the coasts of Taiwan was approximately 170.4 ± 21.02 days. Neither the growth pattern of the otolith nor the age of elvers arriving in the estuary were significantly different among estuaries, indicating that the elvers in both eastern and western Taiwan were probably recruited from the same spawning ground. The growth pattern of the otolith in relation to larval migration was analysed.     

Life history and host specificity of the Japanese flea beetles Trachyaphthona sordida and T. nigrita (Coleoptera: Chrysomelidae), potential biological control agents against skunk vine, Paederia foetida (Rubiaceae), in the southeastern parts of the United States and Hawaii

Skunk vine, Paederia foetida (Rubiaceae), is native to Asia and has been recognized as an invasive weedy vine of natural areas in Florida and Hawaii. Two insects, Trachyaphthona sordida and Trachyaphthona nigrita (Coleoptera: Chrysomelidae) from Japan are being considered as potential biological control agents against skunk vine. To gather fundamental information on their biology, we carried out field surveys and laboratory experiments in Kyushu, southern Japan, between 2003 and 2006. We found that T. sordida is commonly distributed in Kyushu and T. nigrita is restricted to the southern parts of Kagoshima Prefecture on the southern part of Kyushu. These species are fundamentally univoltine and adults appear in late April to early July. Trachyaphthona sordida overwinters as mature larvae and T. nigrita as mature larvae or rarely as adults. Larvae of both species feed on fine roots of P. foetida in the field and Serissa foetida (Rubiaceae) under rearing conditions, and they appear to have tribe‐level host specificity in their host range. On the basis of these results, we suggest that both species are suitable as biological control agents.