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A long-term monitoring programme from 2005 to 2021 has allowed the assessment of age and longevity in an endangered seahorse Hippocampus whitei in the wild. Seahorses were marked using visible implant fluorescent elastomer (VIFE) which allows for individual identification. The longest period from marking to last sighting was 6 years 8 months and 17 days for a female. Using a von Bertalanffy growth function model for the species, this individual would have been approximately 7 years 7 months old on last sighting. These observations suggest that seahorses in the wild can live for over 7 years and demonstrate the benefits of using VIFE in long-term movement, population abundance and life-history studies of seahorses.

The provision of temporary, specially designed artificial habitat may help support populations of the Endangered Whites' seahorse Hippocampus whitei in the face of rapid coastal urbanisation and declining natural habitats. Three designs of artificial habitat (Seahorse Hotels) were installed in Port Stephens, New South Wales, Australia, where natural habitats had significantly declined. Mark recapture surveys were used to assess seahorse site fidelity and population parameters, and the effect of Seahorse Hotel design on seahorse abundance, epibiotic growth and mobile epifaunal seahorse prey was determined. The Seahorse Hotels sustained a substantial population of seahorses (64; 57-72 95% confidence intervals) in comparison to recent local population estimates. There were no significant differences in seahorse abundance, mobile epifauna or epibiotic growth among the three different hotel designs. This research demonstrated that H. whitei will inhabit Seahorse Hotels in absence of natural habitat, and additional complexity in these artificial structures was not necessary to support seahorse populations. Temporary structures such as Seahorse Hotels will be a valuable tool in supporting H. whitei and other Syngnathid populations through infrastructure maintenance or habitat modification.

The endangered seahorse Hippocampus whitei has declined in abundance as a result of natural habitat loss, and inhabits copper-braided protective swimming nets in Sydney Harbour, Australia. This study tested whether the use of copper-free seahorse-friendly net material has any effect on populations of H. whitei. The effects of net material on seahorse density and population abundance, as well as the effects on fouling epibiota and the abundance of epifaunal seahorse prey, were tested on pre-existing swimming nets as well as installed panels of each net material type. Material type had no effect on the density or population abundance of seahorses on pre-existing or installed panels of swimming net, with no difference in fouling epibiotic growth or mobile epifauna. Because seahorse-friendly nets were not worse than standard nets in these respects, it is recommended that managers take a precautionary approach and deploy nets of seahorse-friendly material to minimise anthropogenic copper entering coastal systems.

Analysing the associations between the endangered White's seahorse Hippocampus whitei and characteristics of its environment (including habitat, prey and predator variables) in an estuary in New South Wales, Australia, revealed that seahorses had a greater number of significant associations with environmental correlates within a single seagrass bed than among seagrass beds. Predator abundance was negatively correlated with H. whitei abundances among seven seagrass beds (200-6,000 m apart) and no ecological correlate was associated with H. whitei body size distributions. Within the seagrass bed with the greatest number of H. whitei, individuals preferentially selected locations that were deeper, had denser seagrass, more epiphytic prey types and fewer predators. Smaller H. whitei were associated with greater depths within the bed. In this study, each class of ecological correlate (habitat, prey, predators) was found to have at least one significant relationship with H. whitei, depending on the scale, demonstrating that all three are important to H. whitei populations. As such, future studies that evaluate animal populations may benefit from holistic approaches that consider each of these together. For animals that are experiencing dramatic population declines due to habitat destruction, as H. whitei has over the last decade, a better understanding of its relationship to its environment is important to inform conservation action.

The aim of this study was to determine and compare habitat preferences for male and female adult and juvenile White’s 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

H. whitei Bleeker 1855 English common names. White���s Seahorse, common seahorse, New Holland seahorse, Sydney seahorse. Synonyms. H. novaehollandiae Steindacher 1866; H. procerus Kuiter 2001. Neotype: I.40831-018. Type locality. Sydney Harbour, New South Wales, Australia. Distribution. Australia (east), Solomon Islands. Notes. Meristic and morphological data do not separate purported H. procerus from H. whitei (Appendix O), nor do genetics. Four specimens from Moreton Bay (the type locality for H. procerus) included three haplotypes, each of which was identical to a haplotype from Sydney Harbour (type locality for H. whitei) (H. Hamilton, in litt. to SL and RP, 13 Feb 2015)., Published as part of Sara A. Lourie, Riley A. Pollom & Sarah J. Foster, 2016, A global revision of the Seahorses Hippocampus Rafinesque 1810 (Actinopterygii: Syngnathiformes): Taxonomy and biogeography with recommendations for further research, pp. 1-66 in Zootaxa 4146 (1) on page 43, DOI: 10.11646/zootaxa.4146.1.1, http://zenodo.org/record/268078, {"references":["Bleeker, P. (1855) Over eenige visschen van Van Diemensland. Verhandelingen der Koninklijke Akademie van Wetenschappen, 2, 1 - 30.","Kuiter, R. (2001) Revision of the Australian seahorses of the genus Hippocampus (Syngnathiformes: Syngnathidae) with descriptions of nine new species. Records of the Australian Museum, 53, 293 - 340. http: // dx. doi. org / 10.3853 / j. 0067 - 1975.53.2001.1350"]}

Artificial habitats are a common feature of urban marine environments and usually support different assemblages of marine organisms in contrast to neighbouring natural habitats. Despite these differences, artificial habitats can be managed to benefit biodiversity, either by the addition of structures to provide habitat where little natural habitat remains, or by engineering existing structures to better support native populations. 2. Seahorses are listed as protected species in New South Wales, Australia, and are of conservation concern worldwide. The physical structure of nets used to protect popular swimming beaches in a highly urbanized estuary, Sydney Harbour, was manipulated to test the hypotheses that more structurally complex habitats would support higher abundances of the seahorse Hippocampus whitei that use these structures and their potential prey (mobile crustaceans). 3. The simple addition of frayed net material to construct a more structurally complex net habitat supported higher abundances of H. whitei than unmanipulated nets in a field experiment over 53 days. Habitat preference assays in the laboratory supported the hypothesis that the patterns of distribution observed in the field were due to the preferences of individual seahorses for the more complex habitats. 4. The habitats manipulated to add structural complexity supported much higher abundances of the mobile epifauna (amphipods, copepods) that are consumed by seahorses. The potential therefore exists to engineer artificial structures in urban estuaries to provide habitats that are preferred by vulnerable fauna and their food sources. Copyright # 2011 John Wiley & Sons, Ltd.

1. The fish family Syngnathidae (seahorses, pipefish, pipehorses and seadragons) is fully protected in New South Wales, Australia, but in some countries certain species are threatened by unsustainable collecting, capture as incidental bycatch, and habitat degradation. 2. Within Sydney Harbour, two species of seahorses (Hippocampus abdominalis and Hippocampus whitei) have been found to colonize artificial structures such as jetty pylons and protective netted swimming enclosures. These protective nets are subject to fouling from epibiotic growth (algae, ascidians, bryozoans, etc.) and rubbish, which causes the nets to collapse from the additional weight. Local authorities employ diving contractors on an ad hoc basis to remove the epibiota from nets. 3. Surveys showed a significant decline in the numbers of both seahorse species at one site following the replacement of a net, and recovery of the H. whitei population took more than 15 months. 4. A manipulative experiment tested the importance of epibiotic growth for seahorses. H. whitei, tagged with individual marks, were allocated to sections of a net that had undergone different cleaning procedures. Seahorse size, position on the net and total population abundance were recorded every 2 weeks over a 3 month period. It was demonstrated that seahorses have a significant positive association with epibiotic growth and proximity to the sea floor. Seahorse populations also showed seasonal variation in abundance with increased numbers on the net during the breeding season (spring–summer). 5. This project has led to the development of best practice net cleaning procedures for local authorities in Sydney Harbour to manage growth on the nets while minimizing impacts on seahorse populations. Copyright © 2009 John Wiley & Sons, Ltd.

We provide a quantitative account of local movements in the monogamous Australian species Hippocampus whitei, as a rare report of home range size in fishes living in seagrass habitats. Our study took place in shallow Posidonia seagrass beds in Port Jackson (Sydney Harbour), principally during January to March. Daily monitoring of individual seahorses during underwater observations revealed that both sexes maintained small and apparently undefended home ranges for several breeding cycles at least. Female home ranges were significantly larger than males, when analysed by both the minimum convex polygon and grid cell methods. Home range size was not correlated with either body size or seahorse density. Presumably, home ranges were small in H. whitei because camouflage (to avoid predation and to capture prey), mate fidelity and parental brooding meant they accrued little benefit (and potentially considerable cost) from moving more extensively. Sex differences in home range size may arise from constraints associated with male pregnancy. These fish are among the most sedentary of vertebrates, with relatively small home ranges equalled only by coral reef species. In terms of their conservation, relatively small protected areas may be sufficient to support breeding populations of H. whitei although that limited movement may result in considerable delays in the recolonisation of depleted areas.

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.

The effects of environmental parameters (temperature, feed, stocking density and light levels) on juvenile growth of White's seahorse, Hippocampus whitei, were examined over 107 days. Growth rates in animals stocked at about 3 months old increased with increasing temperature from 0.14 mm day−1 at 17 °C to 0.26 mm day−1 at 26 °C. Several body condition indices fell with increasing temperature, possibly as a result of increased metabolic rates at higher temperatures. The hepatosomatic index (HSI) fell from 4.44 at 17 °C to 2.67 at 26 °C. The gonadosomatic index (GSI) peaked at 20 °C, indicating that the optimal temperature for reproduction was 20 °C. The seahorses became mature at 6–7 months old. The use of Artemia enriched with DC Selco® improved growth rates over non-enriched Artemia, but did not affect the condition indices. There were no major effects of stocking densities (range 0.5–1 seahorse l−1) and light levels (range 24–136 μE m−2 s−1) on growth over the limited range tested, but there was an indication that reproduction might be inhibited at stocking densities greater than 1 seahorse l−1.

Genetic evidence has revealed that sexual fidelity is rather rare in supposedly monogamous animals. Pairing, whether sexually faithful or not, is very uncommon in fish and has not previously been confirmed in fish from seagrass habitats. Here, the first underwater study of seahorse reproduction reveals that males and females of an Australian species (Hippocampus whitei) form pairs that mate repeatedly and exclusively. Partners greet each other daily and eschew interactions with non-partners. Seahorses are unusual in that both sexes provide clear visual evidence of having mated (the male becomes pregnant as the female transfers hydrated eggs) allowing confidence that these fish are sexually faithful to one another. Pairs do not divorce and a pair bond only terminates when one partner disappears. Intra-sexual competition appears not to be important in maintaining pair bonds.

The aim of this study was to collect data on population dynamics and life history for White's seahorse Hippocampus whitei, a geographically restricted species that is listed as data deficient under the IUCN Red List. Data from H. whitei populations were collected from two regions, Port Stephens (north) and Sydney Harbour (south) in New South Wales, Australia, covering most of the known range of H. whitei, from 2005 to 2010. Over 1000 individuals were tagged using fluorescent elastomer and on subsequent recaptures were re-measured for growth data that were used in a forced Gulland-Holt plot to develop growth parameters for use in a specialized von Bertalanffy growth-function model. Growth parameters for Port Stephens were: females L ∞ = 149·2 mm and K = 2·034 per year and males L ∞ = 147·9 mm and K = 2·520 per year compared with estimates from Sydney Harbour: females L ∞ = 139·8 mm and K = 1·285 per year and males L ∞ = 141·6 mm and K = 1·223 per year. Whilst there was no significant difference in growth between sexes for each region, H. whitei in Port Stephens grew significantly quicker and larger and matured and reproduced at a younger age than those from Sydney Harbour. The life span of H. whitei is at least 5 years in the wild with six individuals recorded reaching this age. Data collected on breeding pairs found that H. whitei displays life-long monogamy with three pairs observed remaining pair bonded over three consecutive breeding years. Baseline population densities were derived for two Port Stephens' sites (0·035 and 0·110 m -2) and for Manly in Sydney Harbour (1·050 m -2). Even though the life-history parameters of H. whitei suggest it may be reasonably resilient, precaution should be taken in its future management as a result of its limited geographical distribution and increasing pressures from anthropogenic sources on its habitats. © 2012 The Fisheries Society of the British Isles.