The Environmental Atlas of Abu Dhabi Emirate

161

Proportion of Time Spent at Depth

0.5

0

Day

Night

0.5

A RABIAN G ULF S AILFISH M IGRATION & B EHAVIOUR

0-5 m

5-10 m

10-15 m

15-20 m

20-25 m

Depth

25-30 m

Sailfish belong to a group of fish known as Billfishes, which also include Marlins, Spearfish and Swordfish.

30-35 m

35-40 m

Vertical Habitat Use by Sailfish in the Arabian Gulf Cross Section A-A through Arabian Gulf

40-45 m

45-50 m

All are large predators that possess an elongated rostrum, or bill. Sailfish are further characterised by their enormous dorsal fin resembling a sail, from which their name originates. In the Arabian region, Arabian Gulf Sailfish ( Istiophorus platypterus ) are found from the Red Sea to the Arabian Gulf. The Sailfish is considered a highly migratory species. It is the only billfish normally residing in the Gulf, and aggregates in large numbers off the UAE coast from mid-November to mid-April.

50-80 m

Using satellite archival tags, researchers found that Sailfish spend a majority of their time near the water surface. Sailfish spend most of their day and night at a depth of 0–5 metres; they rarely venture deeper than 30 metres. Sailfish are epipelagic, occupying the upper strata of the oceanic zone where there is enough light for photosynthesis to occur.

Sailfish Track 2

Sailfish Track

Sailfish Track 1

Sailfish Track 3

Sailfish Track

Sailfish Track

May 20th

June 1st

June 11th

Sailfish feed primarily on small schooling fish such as Sardines and Anchovies. They often hunt together forcing the baitfish into a tight ball before attacking with slashing movements of the bill. The Sailfish is a popular sport fish due to its jumping ability and high swimming speeds. This recreational fishery provides important economic benefits to the region. UAE recreational anglers began a self-initiated tag and release programme in 1983. In1998, EAD initiated a conventional tagging programme with the cooperation of volunteer recreational fishermen to understand Sailfish behavioural biology and movements (over 2,000 Sailfish have been tagged).

March 15th

March 27th

June 13th

Sailfish Tracking Sailfish tracks using pop-up satellite archival tags show movement of Sailfish in the Arabian Gulf over select time periods in spring and summer 2002. This, together with conventional tag recovery data, confirms Sailfish occurrence in the Gulf for all months of the year, and therefore validates the presence of a resident Sailfish population in the Gulf.

A

Severe declines in the Sailfish population have been recorded in the waters off the UAE in the past five years due to capture in gillnets and overfishing; the population was nearly eradicated by 2006. Very few Sailfish catches or sightings have been reported by UAE recreational fishermen for the past several years; and, very few catches have been reported from the Iranian gillnet fishery. Unless improved efforts at regional cooperation and joint management strategies are made to conserve the Sailfish, this unique component of biodiversity may face extinction in the Gulf.

A

Sailfish The Sailfish is distinguished by its elongated rigid rostrum or bill and its enormous dorsal fin, which resembles a sail, often stretching along the entire length of its back. Its elongated upper jaw is twice the size of its lower jaw, which contains small file-like teeth. The sailfish is dark blue along the upper half of its body and fades to brownish-blue on the lower sides, to silver-white on its belly. It has 2 dorsal fins and 2 anal fins: the first dorsal sail-like fin, which is the largest, has 42–49 rays and is blue-black with many small black spots; the other fins are silver-blue. The sides of the sailfish contain 15–20 vertical bars lined with small blue spots. This fish can live up to 10 years (average life span is 5–7 years), reach lengths of 3.4 metres and weigh up to 90 kilograms or more. Its sail is usually kept folded down to the side when swimming, and is raised when the sailfish feels threatened or excited; its body colour can also change in response to certain conditions.

Sailfish Migration Patterns in the Arabian Gulf Sailfish are seasonal residents of the Arabian Gulf waters of the UAE, where they aggregate from mid-November to mid-April. Prior to the recent population collapse, they would depart en masse from UAE waters annually, generally in early April, and travel north-west in the Gulf to Iranian waters. Sailfish were found to be vulnerable to incidental capture by Iranian gillnets targeting Kingfish ( Scomberomorus commerson ) and kawakawa ( Euthynnus affinus ). To verify the Sailfish’s summertime location and determine whether the Gulf Sailfish is a resident population, EAD collaboratively deployed pop-up satellite archival tags (PSATs), which relay location data via satellite. Sailfish were found to occur in the Gulf during the summer, indicating they are year-round Gulf residents. To determine if the population was isolated from populations outside the Gulf, DNA tests were conducted and showed that the Gulf Sailfish were an isolated population. This suggests the overall population is strictly limited in terms of its size and capacity to withstand fishing and other pressures.