Striking a balance between retaining populations of protected seahorses and maintaining swimming nets

Abstract

ABSTRACT1. 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.

Seahorse (Hippocampinae) population fluctuations in the Ria Formosa Lagoon, south Portugal

“…Most seahorse species use their prehensile tail as a means to grasp different holdfasts ( e.g . sponges, coral, seagrass, mangrove branches and even artificial structures), thus relying on some degree of habitat structure (Foster & Vincent, ; Harasti et al , ; Hellyer et al , ). Although these fishes are described as sedentary, they can move at least 150 m in a single day (Caldwell & Vincent, ) and can have home ranges of up to 400 m 2 (Garrick‐Maidment et al , ).…”

Monthly population density and structure patterns of an endangered seahorse Hippocampus capensis: a comparison between natural and artificial habitats

“…The higher H. capensis population densities consistently found in the marina is perhaps not surprising, as artificial habitats and structures can increase seahorse population densities (Harasti et al ., ; Correia et al ., ), particularly in areas devoid of natural habitat (Correia et al ., ). Seahorse species found in shallow waters tend to occur in habitats that are protected against adverse environmental effects, such as storms, and which provide suitable habitat in terms of holdfasts (Choo & Liew, ).…”

Artificial structures in sediment-dominated estuaries and their possible influences on the ecosystem

“…The omnipresence of groynes and other artificial structures and habitats in estuaries has not only dramatically changed their morphology and contributed to the loss of natural habitats (Browne and Chapman, 2011;Perkol-Finkel et al, 2012), but has also created many new habitats for benthic and pelagic (Krone et al, 2013;Harasti et al, 2010) species. Previous experimental studies have investigated the invasibility of the artificial materials by nonindigenous invertebrates (Dafforn et al, 2012).…”