Threatened Species of the Week: The Spiny Seahorse
by Lucy Hagger
This weeks threatened species of the week is the Spiny Seahorse (Hippocampus histrix)!
The spiny seahorse is considered vulnerable to extinction under the IUCN classification system due to destruction of their habitat, their trade popularity and vulnerability as by-catch. If you aren’t sure of the classification technique used by the IUCN Redlist then have a look at this post which explains the ins and outs of this system.
Spiny seahorses were previously classed as data deficient. However, after an investigation of the species it was found that they were in decline and this bumped their ranking up to vulnerable. Studies estimated that the world population of spiny seahorses has declined up to 30% in the last 10-15 years, suggesting that they have been under extreme pressure over the last few decades.
The first culprit for this decline is the massive demand for these creatures as pets and for traditional medicine. The populations are being exploited to fulfil this demand and as a result the existing populations are struggling to maintain their numbers. It has been predicted that each year more than 200 000 individuals are traded in parts of the seahorses range and this level of trade is set to continue and potentially increase.
Surveys have also shown that the spiny seahorses are not only becoming rarer, but they also seem to be shrinking. The seahorses that are being caught are smaller than they used to be and this is likely due to the fact that most adult seahorses are rapidly removed from the populations. This leaves more of the smaller juveniles to be caught as many individuals do not survive long enough to reach full maturity before they are caught.
The second major pressure on the spiny seahorse populations is the ever growing issue of by-catch. By-catch are all those unwanted living organisms that are caught in the process of fishing and trawling in the ocean. A huge number of these seahorses are being caught as by-catch throughout the species’ range.
The huge majority of spiny seahorses caught as by-catch are caught as a result of trawling. Trawling involves dragging huge and heavy structures along the seafloor to catch creatures like mussels, clams and oysters. This method is incredibly damaging to the sea floor, basically destroying and removing everything in its path. The spiny seahorses that exist at these depths are swept away with the rest of the sea floor.
By-catch can and should be returned to the ocean. However, due to the huge demand for these seahorses they are generally considered a pleasant surprise as they can be easily sold into the medicine and pet trade. Less damaging trawling methods do exist, however, the majority of these seahorses are being caught in the oceans of developing countries that rarely use these trawlers.
The third threat to these seahorses is habitat destruction; possibly the biggest threat to all biodiversity across the world (but that is another story for another day). As mentioned, these seahorses exist close to the seafloor; specifically at depths of 6-20m. They live on various substrates including sponges, weedy rocky reefs, soft corals but mainly on seagrass beds.
The biggest habitat loss is being seen in seagrasses which are declining as a result of numerous factors. So the first big threat to seagrass is our good friend trawling. Trawling removes the seagrass like it removes the seahorses; leaving the seafloor baron of seagrass. So trawling is threatening spiny seahorses in multiple ways and it could be argued that this is the threat that is the most important to target.
Another threat to the seagrass is eutrophication which occurs when for example fertilisers and sewage leak into water systems. This leads to a massive increase in algae and plankton and therefore an enormous increase in the levels of photosynthesis in these water systems. This removes a significant proportion of the oxygen from the water and therefore starves the other living organisms (including seagrass) that need this oxygen to survive.
Other threats to the seagrass include coastal building which is removing much of the seagrass habitat in those regions. Invasive species are also threatening seagrass; with foreign plants outcompeting the native seagrasses and invasive wildlife consuming it. Overall, the seagrass habitats are under great threat and as a result, so are the spiny seahorses that call these grasses home.
All the threats that face spiny seahorses are predicted to not only continue, but also to worsen. The seahorses may be categorised as vulnerable currently. but it is likely that it will not be too long until they are bumped up to threatened.
Methods are in place to attempt to reduce the impacts of these threats, including stricter control on the seahorse trade. However, with a huge majority of the seahorses being caught as by-catch, it is incredibly difficult to control this trade. More protection is needed for our sea beds, however, the enormous demand for sea life for food, pets and medicinal purposes is meaning that more and more of our seabeds are being trawled and damaged each day.