Abstract
The recent fluctuations in abundance of the Indian oil sardine Sardinella longiceps, a tropical small pelagic clupeid fish, was investigated in the light of overfishing and variations in its habitat ecology in southeastern Arabian Sea. In 2012, its landings peaked to an all-time record making it the fifth largest sardine fishery in the world, and within 3 years the catches were reduced to nearly a tenth of that level. This study examined the fishery dependant factors such as effort, catch rates and expansion of fishing area; the biological variations in fish size, maturity and recruitment; and tried to relate this to the environmental variations in the sardine habitat and food availability. The 2012 mega harvest was a result of a 2-time increase in gear size and engine capacity of fishing crafts and a 3.7-time increase in fishing effort. The female maturation process was strongly influenced primarily by rainfall and then by upwelling and the resulting influx of cold nutrient-rich water in the habitat from April much before the start of the monsoon in June. After 2013, the weak monsoons and the 2015 El Nino Southern Oscillation resulted in a warmer (by an average of 1.1°C) period which negatively impacted the maturation process. The abundance of jellyfishes which are larval and young fish predators in the habitat negatively affected recruitment after 2013. The mismatch in timing of phytoplankton productivity and sardine larvae in the habitat also affected the recruitment success. These environmental divergences coupled with the excessive capture (beyond maximum sustainable yields) of spawning stock and juveniles from 2010 has resulted in this biological catastrophe which has affected the livelihood of thousands of small-scale fishers. A more responsive fisheries administration with timely restriction on fishing effort and protection of spawning stocks by way of fishery closure would have helped minimize the impacts.
Highlights
The Indian oil sardine, Sardinella longiceps, is a small pelagic clupeid fish with distribution limited to tropical waters of northern and western Indian Ocean: Gulf of Aden, Gulf of Oman, but apparently not Red Sea or the Persian Gulf, and eastward to India, including the Andaman Islands
Oil sardines are fished by different craft-gear combinations like, fishing boats with outboard engines using ring seines (OBRS), mechanized units using ring seines (MRS), outboard units using gill nets (OBGN), mechanized trawlers (MTN), outboard units using boat seines (OBBS), other motorized units (MOTRS)
Longhurst and Wooster (1990) have argued that events taking place during the early part of the year, especially March/April, have more influence on success of sardine fishery. We agree with this observation since we have found that the Gonadosomatic index (GSI) starts increasing from these months clearly indicating the relationship between, nutrient enrichment from upwelling followed by diatom bloom leading to maturation
Summary
The Indian oil sardine, Sardinella longiceps, is a small pelagic clupeid fish with distribution limited to tropical waters of northern and western Indian Ocean: Gulf of Aden, Gulf of Oman, but apparently not Red Sea or the Persian Gulf, and eastward to India, including the Andaman Islands. This forage species comes under the group ‘herring, anchovies and sardine, (HAS) which contributes to 18.6% (15.3 million tons) of the global marine capture fishery production (FAO, 2016). With average annual landing of 0.22 million tons during 2001 to 2010, the Kerala State’s landing exceeded the catch from other nations like Oman, Yemen, Iran and Pakistan (FAO, 2016)
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