Km Martin-Smith

Visible implant fluorescent elastomer tagging of the big-bellied seahorse, Hippocampus abdominalis

Abstract Wild and captive management of seahorses often requires individual or batch identification. In seahorses this has proven difficult in the past because of the seahorses’ rigid body structure, reduced size of fins and susceptibility to infection. We investigated the suitability of visible implant fluorescent elastomer (VIFE) for tagging the big-bellied seahorse, Hippocampus abdominalis, Leeson 1827. Thirty-six seahorses were tagged and their mortality, growth and tag retention assessed over a period of 7 months together with 36 control seahorses. No tagged or control animal died. In tagged animals growth rate in standard length (SL) was 6% less than untagged animals (non-significant), and growth rate in weight was 10% less than untagged animals (significant) over the experimental period. No tags were lost during the experiment. Tag visibility under LED blue light did not decline significantly although tag detection with the naked eye decreased significantly over the first month of the experiment. Our results show that VIFE is a highly effective batch tagging method for seahorses with minimal biological effects.

Exploitation and trade of Australian seahorses, pipehorses, sea dragons and pipefishes (Family Syngnathidae)

Seahorses and their syngnathid relatives have provided a focus for efforts to ensure sustainable use of marine resources, with new international trade controls (CITES Appendix II) implemented in May 2004. We demonstrate how a study of international trade can be used to assess relative levels of threat and set domestic research and conservation priorities. Australia has remarkably high syngnathid biodiversity with at least 14 seahorse species, two endemic sea dragon species, and 90 species of pipefishes and pipehorses found in its territorial waters. Our objectives were to quantify species, trade routes, volumes, values and temporal trends in syngnathid trade to and from Australia. We found that Australia is probably the major global supplier of dried pipehorses Solegnathus spp.. These fishes, including at least one endemic species, are sourced from trawl bycatch and comprise Australias largest syngnathid export, by both volume and value. Research is urgently needed to evaluate the impacts and sustainability of trawling on pipehorse populations. Australia is also the sole supplier of two sea dragon species, Phycodurus eques and Phyllopteryx taeniolatus, for the live aquarium trade. Although lucrative, the number of wild-caught individuals involved in this trade was relatively low and probably of low conservation risk relative to habitat loss. Exports of seahorses and other pipefish species, and imports of all syngnathid species, are minor on a global scale, although the burgeoning aquaculture industry for seahorses requires careful evaluation for its potential impacts on wild populations.

Genetic monogamy despite social promiscuity in the pot-bellied seahorse (Hippocampus abdominalis)

Sexual selection theory predicts a positive correlation between relative parental investment and mate choice. In syngnathid fishes (seahorses and pipefish), males brood offspring in specialized brooding structures. While female‐female mating competition has been demonstrated in some pipefishes, all seahorses (genus Hippocampus) studied to date have been found to have conventional sex roles with greater male–male competition for access to mates despite possessing the most complex brood structures in the family. Although multiple mating is common in pipefish, seahorses are again exceptional, exhibiting strict genetic monogamy. Both demographic and behavioural explanations have been offered to explain the lack of multiple mating in seahorse species, but these hypotheses have not yet been explicitly addressed. We investigated mating systems and brood parentage of the pot‐bellied seahorse, Hippocampus abdominalis, a temperate‐water species that is socially promiscuous with conventional sex roles in laboratory populations. We observed promiscuous courtship behaviour and sex‐role reversal in high density, female‐biased field populations of H. abdominalis. We hypothesize that sex roles are plastic in H. abdominalis, depending on local population density and sex ratio. Despite promiscuous courtship behaviour, all assayed male seahorses were genetically monogamous in both laboratory and wild populations. Physiological limitations associated with embryo incubation may explain the absence of multiple mating in seahorses and may have played an important role in the development of the unique reproductive behaviour typical in these species.

Ontogenetic and sex-based differences in habitat preferences and site fidelity of White's seahorse Hippocampus whitei

The aim of this study was to determine and compare habitat preferences for male and female adult and juvenile Whites seahorse Hippocampus whitei and assess their movements and site fidelity over 4 years. Data were collected from three sites along 1.5 km of estuarine shoreline in Port Stephens, New South Wales, Australia, from 2006 to 2009 using H. whitei that had been tagged with visible implant fluorescent elastomer. Relative availability of 12 habitats and habitat preferences of H. whitei was determined, based on the habitat that H. whitei used as a holdfast. Hippocampus whitei occurred in nine different habitats; adults preferred sponge and soft coral Dendronephthya australis habitats with no difference between male and female habitat preferences whilst juveniles preferred gorgonian Euplexaura sp. habitat. There was a significant preference by adults for D. australis colonies with height >40 cm and avoidance of colonies <20 cm. Neither adults nor juveniles used sand or the seagrasses Zostera muelleri subsp. capricorni and Halophila ovalis. Hippocampus whitei showed cryptic behaviour with c. 50% of adult sightings cryptic and c. 75% for juveniles with crypsis occurring predominantly in Sargassum sp. for adults and Euplexaura sp. habitat for juveniles. Within sites, females moved significantly longer distances (maximum of 70 m) than males (maximum of 38 m) over 20 months. Strong site fidelity was displayed by H. whitei with males persisting at the same site for up to 56 months and females for 49 months and no H. whitei moved between sites. The longest period that an H. whitei was recorded on the same holdfast was 17 months for a male and 10 months for a female. As this species displays strong site fidelity, specific habitat preferences and has a limited distribution, future management needs to minimize the risk of habitat disturbance as loss of key habitats could have a negative effect on species abundance and distribution.

Photo‐identification of individual weedy seadragons Phyllopteryx taeniolatus and its application in estimating population dynamics

Forty-three individual adult weedy seadragons Phyllopteryx taeniolatus were identified from underwater images using patterns of spots and blotches on the lateral surface of the abdomen. These patterns were unique and did not change over the 18 month course of the study and could therefore be used to identify individuals when estimating population variables using non-invasive capture-mark-recapture and accumulation curve methods. Two similar neighbouring sites in southern Tasmania showed considerable differences in their estimated populations of P. taeniolatus. Estimated annual survival was >80% at one site suggesting that P. taeniolatus may be considerably longer lived than other syngnathids with a maximum life span in excess of 10 years. Males incubating embryos were observed from October to March and at least two clutches could be borne during this period. This technique of photo-identification could provide a cheap and effective way to monitor populations of this iconic species across its range, particularly in conjunction with optimized pattern-recognition software.

Does a no-take marine protected area benefit seahorses?

Seahorses are iconic charismatic species that are often used to ‘champion’ marine conservation causes around the world. As they are threatened in many countries by over-exploitation and habitat loss, marine protected areas (MPAs) could help with their protection and recovery. MPAs may conserve seahorses through protecting essential habitats and removing fishing pressures. Populations of Whites seahorse, Hippocampus whitei, a species endemic to New South Wales, Australia, were monitored monthly from 2006 to 2009 using diver surveys at two sites within a no-take marine protected areas established in 1983, and at two control sites outside the no-take MPA sites. Predators of H. whitei were also identified and monitored. Hippocampus whitei were more abundant at the control sites. Seahorse predators (3 species of fish and 2 species of octopus) were more abundant within the no-take MPA sites. Seahorse and predator abundances were negatively correlated. Substantial variability in the seahorse population at one of the control sites reinforced the importance of long-term monitoring and use of multiple control sites to assess the outcomes of MPAs for seahorses. MPAs should be used cautiously to conserve seahorse populations as there is the risk of a negative impact through increased predator abundance.