Fish resources assessment survey of the Arabian Sea coast of Oman

A primary aim of the Sultanate of Oman Ministry of Fisheries Wealth is to ensure that fisheries are developed and managed for the advantage of the people of Oman in a manner that is sustainable and maintains biodiversity.

The problem

A primary aim of the Sultanate of Oman Ministry of Fisheries Wealth is to ensure that fisheries are developed and managed for the advantage of the people of Oman in a manner that is sustainable and maintains biodiversity.

The ministry needed estimates of the fishable biomass of principal fish species off the Arabian Sea coast of Oman to guide development and investment decisions.

It hired a New Zealand-led consortium to conduct a series of fisheries surveys covering the key species in the area. The surveys focused on three broad groupings of fish:

  • Demersal fish: bottom feeders.
  • Small pelagic fish: small ‘free swimming’ fish that live and feed in the pelagic zone, which is a broad zone of water below the sea surface but above the bottom.
  • Mesopelagic fish: fish that live in the ‘twilight’ part of the pelagic zone where it is not completely dark but there is too little light for photosynthesis.

NIWA staff led the development of the survey methodology and carried out the at-sea scientific and technical work with assistance from Omani staff.

A complex fishery

Fisheries in Oman are complex with a wide range of species being taken by a wide range of methods.

According to statistics published by the Ministry of Fisheries Wealth, total estimated landings in 2005 were 157 322 metric tonnes, made up of 24 710 mt attributed to “industrial” fishing and 132 612 attributed to “traditional” fishing. The catch consisted of 45 221 mt of large pelagics, 48 729 mt of small pelagics, 40 698 mt of demersal fish, 5630 mt of sharks and rays and 12 500 mt of invertebrates (including lobsters and abalone).

The area surveyed is a major fisheries region for Oman. There is approximately 1200 km of Omani coast on the Arabian Sea, extending from Ra’s Al Hadd in the north to the Oman-Yemen border in the south. This area is characterised by significant shallow coastal waters, a moderate area of continental shelf, and a steep continental slope, which is very close to the coast in the south.

No comprehensive surveys since 1990

Surveys of demersal, small pelagic and mesopelagic fish were conducted between 1963 and 1990. The most extensive of these were from RV Dr Fridtjof Nansen (Norwegian Agency for International Development and FAO, 1975, 1976, 1983–84) and FRV Rastrelliger (in 1989–90). Clearly the Ministry of Fisheries Wealth needed much more up-to-date information on which to base its decisions.

Need to test whether catches were exceeding yields

Estimates of potential yield of demersal fish in 1995 suggested that at that time catches were close to or exceeding yields. Catches increased from 35,000 mt in 1995 to over 40,000 mt in 2005.

Similar conclusions were made for small pelagic fish, although some allowance needed to be made for the significant quantities of small pelagic fish found in shallow areas which were not surveyed. Catches of small pelagics increased from around 41,000 mt in 1995 to 49,000 mt in 2005.

Need to understand seasonal patterns

Fisheries productivity in the region is heavily influenced by at least two seasonal factors:

  • the monsoonal winds, particularly the Southwest monsoon, which generates upwelling of nutrient rich waters which enhances productivity, particularly in the northern part of the area.
  • the seasonal development of an oxygen deficient layer in depths between about 50 and 1000m in which most fish species cannot live.

The solution

The specific objectives of this project were:

  • To provide good quality estimates of biomass fish of the Arabian Sea of Oman coast as a basis for future development and for comparison with future surveys.
  • To provide estimates of stock size, seasonal distribution and abundance for selected target species, by using bioacoustic and survey fishing, as a basis for stock assessments of these species.
  • To collect pertinent biological information and samples in both traditional and commercial fishing areas to assist in description of the biology and stock assessment of these species.
  • To provide information on the other species collected during the survey as a basis for conservation of biodiversity in the Arabian Sea.
  • To provide oceanographic information that will contribute to an understanding of the biodiversity and ecological dynamics of the Arabian Sea and Indian Ocean, specifically in relation to the seasonality, distribution and abundance of fishery resources.
  • To provide spatial habitat information that will support development of spatially related management opportunities.
  • To explore traditional fishing grounds for less exploited but nonetheless valuable resources.
  • To investigate the existence of new fishing grounds, including those for benthic resources, which might be beneficially exploited by local fisherfolk, such as marine invertebrates and fishery resources beyond 250m depths.

Five surveys conducted

Five seasonal surveys with an average duration of 47 days were completed in the project period using the RV Al Mustaqila 1. The surveys were timed to ensure coverage of the main seasons, with an overlap of one season, between August 2007 and September 2008.

The survey design and activities were focused on the three key resource groups: demersal fish, small pelagic fish, and mesopelagic fish. However, the survey activities were tightly integrated within each voyage to ensure appropriate data was obtained to address the full range of objectives.

Making best use of old data

The previous surveys (1963-1990) provided a good base for designing a new survey series for abundance and seasonal distribution with greater precision. We tried to ensure as much compatibility as possible between our surveys and the previous ones, so that we could evaluate any changes in fish abundance and distribution over the last two decades – at least where suitably informative data were available from the earlier surveys.

RV Al Mustaqila 1

The survey vessel used is 45.2 metres long, and was equipped to carry out the required sampling, including bottom and mid-water trawling, acoustic surveys using scientific echo-sounders, and collection of oceanographic and bathymetric data.

The result

During the five surveys, we completed a total of 238 days at sea, covering all the main seasons including the bi-annual monsoons that produce large seasonal variations in fish movement and catches.

While at sea, we:

  • Conducted survey trawls in 614 locations
  • Conducted exploratory trawls in 44 locations
  • Conducted mark identification trawls in 284 locations (to check interpretation of the ‘marks’ made by fish picked up on the ship’s echo-sounder during acoustic surveying)
  • Created 6071 acoustic files
  • Deployed the CTD instrument 1400 times (to measure basic properties of the ocean, including conductivity and temperature at various depths)
  • Recorded underwater video footage at 146 locations
  • Set fish traps at 113 locations

Each survey lasted an average of 47 days, but that was just a fraction of the work involved in this project.

The full series of reports and technical appendices for Oman’s Ministry of Fisheries Wealth ran to over 1000 pages. The detailed contents are confidential to the client. The ministry is now using the data we collected, and the abundance estimates we made, to inform their fisheries management decisions.

During the surveys, we found more than 500 species of fish. Some of these species had not been recorded in Omani waters before, and some may be new to science. These species will be described by taxonomists in coming years.

In more detail, the surveys:

  • Measured 213 363 fish and invertebrates
  • Collected biological data from 99 319 fish (at least length and weight)
  • Recorded 445 fish and shark species or species groups, of which 91 are potential new records for Oman
  • Recorded 110 non-fish species or species groups of invertebrates, including cuttlefish, squids, and benthic invertebrates (living on the seafloor)
  • Caught 3 species of turtle on 10 occasions, all of which were released alive and unharmed.