Norman G. Hall

Reproductive Biology and Protandrous Hermaphroditism in Acanthopagrus latus

Detailed macroscopic and histological studies of the gonads of a full size and age range of Acanthopagrus latus from each season in Shark Bay, Western Australia, demonstrate that this species is a protandrous hermaphrodite in this large subtropical embayment. Although our scheme for the changes that occur in the ovotestes of A. latus during life is not consistent with some of the conclusions drawn for this species elsewhere, it is similar to that of Pollock (1985 J. Fish. Biol. 26: 301–311) for the congeneric Acanthopagrus australis. The ovotestes of males develop from gonads which contain substantial amounts of both testicular and ovarian tissue. The testicular component of the ovotestes of all males regresses markedly after spawning. During the next spawning season, the ovotestes either become gonads in which the testicular zone again predominates and contains spermatids and spermatozoa (functional males), or gonads in which the ovarian zone now predominates and contains mature oocytes (functional females). Once a fish has become a functional female, it remains a female throughout the rest of its life. In Shark Bay, A. latustypically spawns on a limited number of occasions during a short period in late winter and early spring and has determinate fecundity. The mean potential annual fecundity was ca. 2 000 000. The total length of 245 mm, at which, during the spawning period, 50% of A. latus become identifiable as males, is very similar to the current minimum legal length (MLL) of 250 mm, which corresponds to an age of ca. 2.5 years less than that at which 50% of males become females. Thus, although the spawning potential ratio suggests that the present fishing pressure is sustainable, the current MLL should be reviewed if recreational fishing pressure continues to increase.

Spatial variation in life history characteristics of snapper (Pagrus auratus) within Shark Bay, Western Australia

Abstract Life history characteristics of snapper (Pagrus auratus) were found to vary at fine spatial scales (less than tens of kilometres) in the sub-tropical waters of Shark Bay, Western Australia, from research undertaken between 1997 and 2004. Differences in the timing and duration of the spawning season, length and age at maturity, and maximum age and growth between snapper from the Eastern Gulf, Denham Sound and Freycinet Estuary were attributed to spatial differences in environmental conditions and density-dependent responses to fishing-induced changes in spawning biomass. Such fine-scale spatial variation in the biological characteristics of snapper is consistent with results of previous stock identification studies and further supports the geographic scale at which local snapper stocks are managed to protect both stock productivity and genetic diversity.

Growth and reproductive biology of the foxfish Bodianus frenchii, a very long‐lived and monandric protogynous hermaphroditic labrid

Samples of the foxfish Bodianus frenchii, collected over reefs on the lower west and south coasts of Western Australia, contained individuals ranging up to 78 years old. Although B. frenchii is far smaller than many other species within the Labridae, its maximum age is the greatest yet recorded for this highly speciose family and, together with Achoerodus gouldii, provides an example of a temperate hypsigenyine with exceptional longevity. Length and age compositions of females and males and the histological characteristics of gonads of a wide length range of individuals demonstrated that B. frenchii is a protogynous hermaphrodite. Furthermore, as, on both coasts, the length of the smallest male was greater than that at which all females had become mature, B. frenchii is a monandric protogynous hermaphrodite, i.e. all of its males are derived from functional females. Attainment of maturity by females is related more to length than age, whereas the reverse is true for sex change. On the basis of Schnute growth equations and length-to-body mass regression equations, the predicted length at age and body mass at length of fish on the south coast were greater than those on the west coast throughout life. Although B. frenchii spawns daily during the main spawning season, which extends from October to February on both coasts, its fecundity at any given length is substantially greater on the south than on the west coast. The more rapid growth of juveniles and earlier attainment of maturity by B. frenchii on the south coast than on the warmer west coast, together with maturation at a similar size on both coasts, run counter to the trends observed in many species and certain ecological theories regarding the relationships between life-cycle traits and latitude and temperature. The attainment by B. frenchii of a larger body length at age, of greater body mass at length and of greater fecundity at both length and body mass in fish on the south than on the west coast strongly suggests that conditions on the former, cooler coast are more favourable for this labrid, which belongs to a sub-genus whose other species typically live in cool, deep, temperate waters.

Expanding Aerial-Roving Surveys to Include Counts of Shore-Based Recreational Fishers from Remotely Operated Cameras: Benefits, Limitations, and Cost Effectiveness

Abstract Information on shore-based recreational fishing is essential for the sustainable management of nearshore fish stocks. However, obtaining estimates of catch and effort from such fishing activity can be complex and expensive due to the large spatial scales over which surveys are typically conducted and the fine-scale temporal resolution that is desired. Complementary surveys are one option for improving the accuracy of estimates. A pilot study was conducted in Perth, Western Australia, from April to June 2010 to test an expanded aerial–roving survey design that incorporated remotely operated cameras. Cameras recorded the distribution of shore-based fishing activity across a 24-h day, highlighting an afternoon peak as well as some nighttime activity, which is rarely captured in existing survey designs. This information was combined with instantaneous counts of shore fishers from aerial surveys and trip length data that were obtained from 1,194 incomplete trip interviews conducted during roving creel...

Comparisons of the Growth and Gonadal Development of Otolith-Stained, Cultured Black Bream, Acanthopagrus butcheri, in an Estuary with Those of Its Wild Stock

Acanthopagrus butcheri was cultured from broodstock from a southwestern Australian estuary in which its abundance had declined. After marking their otoliths with alizarin complexone, the cultured juveniles were released into this estuary at 6 months of age. Regular sampling demonstrated that this stain persisted throughout the next 3.5 years and that, during the last two of those years, cultured fish dominated the black bream assemblage. Cultured fish grew slower than wild fish, with females reaching total lengths of about 182, 220, and 243 mm at 2, 3, and 4 years, respectively, compared with about 199, 248, and 286 mm in wild fish. However, cultured A. butcheri grew faster than wild A. butcheri in most other estuaries studied. By 3 years of age, essentially all wild fish, but only some restocked fish, had matured. Cultured females matured at a similar length but at an older age than wild females, and cultured males matured at both a greater length and older age than wild males. We conclude that cultured A. butcheri can be used to increase the abundance of a depleted stock, but the reason for the slightly reduced performance of cultured fish should be elucidated and overcome.

Long-term monitoring of boat-based recreational fishing in Shark Bay, Western Australia: providing scientific advice for sustainable management in a World Heritage Area.

Effective management of a recreational fishery must include long-term monitoring programs that allow determination of trends in temporal and spatial variability of catch and effort data. Such monitoring becomes of inherently greater importance when managing a recreational fishery in a World Heritage Area, such as Shark Bay, Western Australia. Between 1998 and 2010, 11 12-month bus-route surveys of boat-based recreational fishing were undertaken at three key boat ramps in Shark Bay. These surveys demonstrated that, in response to the progressive implementation of new management measures, the estimated annual recreational fishing-boat effort decreased by 46%. As a consequence, the estimated annual retained and released catches of the key species, pink snapper (Pagrus auratus), declined and the proportions of the catches of this species that were released each year increased. Annual catches of other species also declined, however, the composition of species retained and released each year varied. The study demonstrated that monitoring of the recreational fishery within Shark Bay provided both immediate and longer-term data on the responses by recreational fishers to changes in management. This produced the information necessary to assess the effectiveness of management measures that were introduced and to modify these as required.

Do the maximum sizes, ages and patterns of growth of three reef‐dwelling labrid species at two latitudes differ in a manner conforming to the metabolic theory of ecology?

The size and age data and patterns of growth of three abundant, reef-dwelling and protogynous labrid species (Coris auricularis, Notolabrus parilus and Ophthalmolepis lineolata) in waters off Perth at c. 32° S and in the warmer waters of the Jurien Bay Marine Park (JBMP) at c. 30° S on the lower west coast of Australia are compared. Using data for the top 10% of values and a randomization procedure, the maximum total length (L(T) ) and mass of each species and the maximum age of the first two species were estimated to be significantly greater off Perth than in the JBMP (all P < 0.001) and the maximum ages of O. lineolata in the two localities did not differ significantly (P > 0.05). These latitudinal trends, thus, typically conform to those frequently exhibited by fish species and the predictions of the metabolic theory of ecology (MTE). While, in terms of mass, the instantaneous growth rates of each species were similar at both latitudes during early life, they were greater at the higher latitude throughout the remainder and thus much of life, which is broadly consistent with the MTE. When expressed in terms of L(T), however, instantaneous growth rates did not exhibit consistent latitudinal trends across all three species. The above trends with mass, together with those for reproductive variables, demonstrate that a greater amount of energy is directed into somatic growth and gonadal development by each of these species at the higher latitude. The consistency of the direction of the latitudinal trends for maximum body size and age and pattern of growth across all three species implies that each species is responding in a similar manner to differences between the environmental characteristics, such as temperature, at those two latitudes. The individual maximum L(T), mass and age and pattern of growth of O. lineolata at a higher and thus cooler latitude on the eastern Australian coast are consistent with the latitudinal trends exhibited by those characteristics for this species in the two western Australian localities. The implications of using mass rather than length as the indicator variable when comparing the maximum sizes of the three species and the trends exhibited by the instantaneous growth rates of those species at different latitudes are explored. Although growth curves fitted to both the L(T) and masses at age for the males of each species lay above those for their females, this would not have influenced the conclusions drawn from common curves for both sexes.

Comparisons between the biology of two co-occurring species of whiting (Sillaginidae) in a large marine embayment

SynopsisWe compare the biology of the tropical species Sillago analis and the temperate species Sillago schomburgkii in Shark Bay, a large subtropical marine embayment on the west coast of Australia. This environment constitutes approximately the southernmost and northernmost limits of the distributions of these two species, respectively. The annuli visible in sectioned otoliths of S. analis and S. schomburgkii form annually. Their numbers were thus used to age the individuals of these two species, which are morphologically very similar and live in the same habitats. Although the growth rates of S. analis and S. schomburgkii are very similar until maturity is attained, they subsequently diverge, with S. schomburgkii investing relatively more energy into somatic growth. The maximum total lengths and ages of both the females (320 mm, 6 years) and males (283 mm, 8 years) of S. analis were not as great as those of the females (383 mm, 9 years) and males (302 mm, 9 years) of S. schomburgkii. In Shark Bay, S. schomburgkii spawns earlier and longer than S. analis, i.e. August–December vs. January–March, which would result in the juveniles of these two species recruiting into nursery areas at different times. In addition, S. schomburgkii spawns earlier and for longer in Shark Bay than in temperate marine waters 800 km further south, presumably reflecting the fact that, in that subtropical embayment, water temperatures over which this species typically spawns are attained earlier and last for longer. However, although environmental conditions in Shark Bay and those temperate marine waters differ markedly, the growth of the corresponding sexes of S. schomburgkii in these two water bodies is similar.

Biology of the silky shark Carcharhinus falciformis (Carcharhinidae) in the eastern Indian Ocean, including an approach to estimating age when timing of parturition is not well defined

Biological data were recorded for 1265 silky sharks Carcharhinus falciformis collected from fish landing sites in eastern Indonesia. These represented catches taken in most calendar months by gillnetting and longlining in the eastern Indian Ocean and contained individuals ranging from embryos to fully mature adults. The growth zones in centra, which were shown to form annually, were counted in the vertebrae in a sub-sample of 200 fish for ageing purposes. The embryo lengths in the 5 months for which there were such data, and the presence of neonates in virtually all months, however, indicated that birth occurs throughout the year and thus there was no well-defined birth date for ageing individual fish. The approximate birth date of each individual was thus estimated from a combination of the total length (L(T) ) at capture and backcalculated L(T) at the formation of the birth zone and at the first and last growth zones in the vertebral centra, together with the period that had elapsed between the formation of those last two growth zones. The number of eggs or embryos in uteri ranged from two to 14, with a mean of 7·2. The estimated mean L(T) at birth of females (811 mm, range: 799-823 mm) and males (812 mm, range: 794-830 mm), derived from the backcalculations corresponding to the birth zones in the centra, were not significantly different (P > 0·05). The L(T) ranges in the catches of post-natal females (570-2592 mm) and males (553-2289 mm) taken by gillnetting were wider than those of the females (1177-2623 mm) and males (1184-2409 mm) taken by longlining. The oldest female and male were 19 and 20 years-old, respectively. The von Bertalanffy growth curves for the two sexes did not differ significantly. The growth coefficient, k, and the asymptotic length, L(T∞). were 0·066 year⁻¹ and 2994 mm for the curve fitted to the combined data for females and males. The lengths L(T50) and ages A(50) at which C. falciformis attained maturity were 2156 mm and 15 years for females and 2076 mm and 13 years for males. The very high proportion of C. falciformis with lengths

Size compositions and reproductive biology of an important bycatch shark species ( Heterodontus portusjacksoni ) in south-western Australian waters

Heterodontus portusjacksoni was obtained from the catches of commercial trawl, gillnet and longline fisheries operating in south-western Australian waters, in which this shark is an abundant bycatch species. Ninety per cent of the H. portusjacksoni caught by commercial trawling in a marine embayment were 400 mm. Although the differences between the size compositions in the catches obtained by trawling vs both gillnetting and longlining, which were similar, are partly attributable to gear selectivity, they also reflect a use by juvenile H. portusjacksoni of protected nearshore waters as nursery areas and a tendency for larger juveniles and adults to occupy reef/rock habitats in a range of water depths. The fact that all but one of the numerous H. portusjacksoni >800 mm were females is reflected in the ratio of females to males differing significantly from parity in the gillnet and longline samples. Yolked oocytes usually take one year to develop to ovulatory size. Ovulation occurs in late winter to early summer and hatching takes place a year later when the embryo is 180–220 mm. The claspers of males commence rapid growth at a total length of ~450 mm, coincident with the onset of clasper calcification and gonadal maturation. The rate of clasper growth relative to total length reached a maximum at ~570 mm and then declined precipitously as the claspers approached full calcification. Based on gonadal criteria, the L50 at maturity for females (805 mm) was nearly 40% greater than that for males (593 mm). Values of the deviance information criterion and marked overlap in their 95% confidence intervals demonstrate that the L50 of 581 mm derived for males using full clasper calcification as the index of maturity was equally valid as the above L50 derived for males at maturity using gonadal criteria. The capture of substantial numbers of juveniles by trawling and of females