Seahorses as an index of global fishing pressure

When I discuss the need to manage seahorse catch with government officials, they often tell me that fishers only report getting a few seahorses per trip, so what’s the big deal?

The big deal is that there are A LOT of fishing trips. So many trips that catching just a few seahorses per trip adds up to more than 70 million. It’s not surprising that fishers report catching few seahorses per fishing trip. Seahorses typically occur in low densities and are patchy in their distribution. Moreover, people have been fishing seahorses for a long time, such that they are now generally rare even in areas where they were once abundant.

What’s vital to realise is that, although individual boats might catch just a few per day¹, the cumulative catch is huge. There are just so many boats fishing on so many days. As one example, in Thailand we estimated that almost 44,000 boats catching a mean of 0.5 to 18 seahorses per day (depending on gear type), resulted in an annual catch of 29 million seahorses². As another example, we estimated that 14,363 boats in Viet Nam (just in provinces where we had data) catching 0.5 to 15 seahorses per day (again, depending on gear type), together caught nearly 17 million seahorses per year³. In both countries the actual catch was certainly much higher than these already high estimates: (1) there are more vessels than we documented; (2) there are more gears than we documented; (3) more provinces catch seahorses than we documented; and, (4) there are more gear/province combinations than we documented.

Five years ago, we carried out a study to estimate the total seahorse catches across the globe⁴.  This meant tallying up catch estimates from the trade surveys we had done across five gear types and 21 countries. That’s just half the countries where we knew seahorses are caught, where our data were best⁵.

We found that seahorse bycatch across all five gear types amounted to just under one seahorse per vessel per day.

Stunningly, fleet sizes were so huge that annual catches were then estimated at approximately 37 million seahorses across our sampled countries.

We have since update this global estimate with more recent data (details below).

Our updated estimate of total catch now sits at 76 million individual seahorses annually from just these 21 best assessed countries. Yikes.

Seahorses provide us with an index of global fishing pressure: their small daily catch rates add up to such a large number in a direct reflection of the huge amount of fishing pressure being exerted on the coastal seas where seahorses live.

For seahorses as for many other species, big catches mean big problems. Because no countries carry out long term monitoring of their seahorse catches, we rely on stakeholder interviews to understand changes over time. Our trade surveys indicate population declines for most species of seahorse involved in international trade. Indeed, overfishing has led to at least 12 species declining in number by at least one third over the last 10 years⁶.

A huge proportion of our estimated global total is caught by bottom trawls⁷. These destructive gears drag heavy nets across the ocean floor catching everything they encounter and destroying habitats along the way. They are among the most irresponsible fishing gears. Those that catch seahorses are largely unregulated and their catch goes unreported. And a LOT of trawlers fish a lot of the time – an estimated 83,000 in Asian countries alone⁸.

Because trawlers have largely destroyed the oceans where they fish, their catches are not profitable enough to keep them afloat. Instead governments use public money, our money, to keep them fishing⁹. This year the World Trade Organisation is hoping to reach an agreement to put an end to these kinds of fishing subsidies – those that are leading to the emptying of our oceans. Such an agreement would rein back global fishing pressure – helping save seahorses and so much more.

Bottom line: a few seahorses per trip is a VERY big deal. Now imagine what is happening to species caught in larger number per trip. Our seahorse index of fishing pressure speaks for a great deal of other marine life.

We’re determined to bring down this tally of seahorses in fishing nets.

You can help:

• Choose your seafood wisely – avoid trawled seafood & farmed shrimp
• Push for more protected areas that work effectively
• Demand an end to:
  • bottom trawling – the waste of life is atrocious
  • harmful subsidies – we are paying to keep unprofitable fisheries afloat
  • illegal, unreported and unmanaged fisheries
  • illegal wildlife trade

Methods used to update catch estimate:

Step 1 – We extracted the median annual catch estimates for the countries where we have carried out trade research post 2015.

• India: ~14 million seahorses (data from 2015-2017 )¹⁰[10]
• Philippines: ~1.7 million seahorses (data from 2019)¹¹
• Senegal: ~370,000 seahorses (unpublished data from 2012 and 2013, but analysed after 2015)
• Thailand: ~29 million seahorses (data from 2013 and 2014)¹²
• Viet Nam: ~16.7 million seahorses (data from 2016)¹³

Step 2 – We took the median estimated annual bycatch volume from our 2015 study (published in 2017, ~ 37 million individuals) and subtracted the catch estimates used in that study for the five countries for which we have more recent information. In so doing we removed ~24 million individuals across the five countries in Step 1, above. This left an estimated catch for the 15 countries for which we do not have more recent data – ~13.5 million individuals.

Step 3 – We added the median annual catch estimates from Step 1 and 2 together. Our estimated global seahorse catch volume now sits at 76 million individuals across 21 countries.

1. The median catch per unit effort of seahorse bycatch across 21 countries and five gear types was 0.96 seahorses per vessel per day. Lawson et al. 2017
2. Fleet size reported for otter trawls, pair trawls, purse seines, pushnets, gillnets and cages on both the Andaman and Gulf of Thailand coasts, Aylesworth et al. 2017
3. Provincial data for crab nets, divers, seine nets, single trawls and pair trawls, Foster et al. 2017.
4. Lawson et al. 2017
5. For example in SE Asia we know Cambodia and Indonesia trawls catch seahorses – but we did not have catch estimates to include in this analysis
6. IUCN Red List
7. E.g. 67% of the total estimated seahorse catch in Thailand was from otter and pair trawls, Aylesworth et al. 2017; 95% of the total estimated seahorse catch in Viet Nam was from otter and pair trawls, Foster et al. 2017. (See [2] and [3])
8. Funge-Smith, S., Brigs, M. and Miao, W. (2012) Regional overview of fisheries and aquaculture in Asia and the Pacific 2012. Asia Pacific Fisheries Commission RAP Publication 2012/26. 154pp.
9. E.g. Half of all shrimp landings came from countries with subsidies on fuel, Sumaila, U. R., Teh, L., Watson, R., Tyedmers, P. and Pauly, D. (2008) Fuel price increase, subsidies, overcapacity, and resource sustainability. ICES Journal of Marine Science. 65: 832-840; Without fuel subsidies, more than 90% of China’s fishing vessels would lose money, Guo 2015 as cited in Zhang, W., Liu, M., Sadovy de Mitcheson, Y., et al (2020). Fishing for feed in China: Facts, impacts and implications. Fish and Fisheries. 21:47–62.
10. Vaidyanathan and Vincent, in revision
11. Foster et al. 2019
12. Aylesworth et al. 2017
13. Foster et al. 2017