Studies on major small pelagic fishes along the Kerala Coast with respect to the Potential Fishery Zone (PFZ) advisories

Nair, Preetha G (2015) Studies on major small pelagic fishes along the Kerala Coast with respect to the Potential Fishery Zone (PFZ) advisories. Doctoral thesis, Central Marine Fisheries Research Institute.

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    Indian National Centre for Ocean Information Services (INCOIS), Hyderabad, India provides fishery forecast services all along the Indian coast free of cost, referred to as ‘Potential Fishery Zone (PFZ) Advisories’. These services include georeferenced maps showing marked regions where probability of finding sizeable schools of fishes is high. These advisories are provided to help the fisher folks to improve their income from fishing by saving engine fuel for searching and locating fish stocks. Based on 124 controlled fishing experiments carried out in the PFZ and Non-PFZ zones along the Kerala coast during 2008-2012 periods, the present study evidenced that commercially important fishes were abundant in the PFZ, forming richer fisheries compared to the non-PFZ areas. The profit from controlled experiments showed consistently higher values in the PFZ than that in the non-PFZ. The highest profit during the entire controlled fishing experiments was obtained when the catch was dominated by relatively high-priced fishes such as tunas, carangids, seer fishes and mackerel. Indian oil sardine was the major single species obtained during the Northeast Monsoon (November-February), whereas, Indian mackerel dominated during the Southwest Monsoon (June-October) and Spring Intermonsoon (March – May) periods. Anchovies were found to dominate only in two fishing experiments in the entire study period. The analyses of catch data of the small pelagic fishes of interest (Indian oil sardine, Indian mackerel and Commerson’s anchovy) showed that the PFZ advisories better predicted the catches of Indian oil sardine during the Northeast Monsoon (November- February) and Indian mackerel during the rest of the period. Conversely, the catch data of controlled experiments showed that PFZ advisory has less efficiency to support the exploitation of anchovies. Attempts have been made to outline the recurrent PFZ along the Kerala coast based on the advisories generated for the study period (2008-2012). Altogether 432 PFZ advisories were digitised and month-wise repeat PFZs have been demarcated. In general, most of the very prominent recurrent PFZs were found within the 50m depth contour. The highest number of recurrent PFZs was in December, January and February. On the other hand, the lowest number of recurrent PFZs was found in April, May and June. Plankton components in the diet of Indian oil sardine, Indian mackerel and Commerson’s anchovy based on fortnightly fish samples analysed during a year period are presented. Coscinodiscus, Nitzschia, Pleurosigma and Thalassiosira were found in the gut of Indian oil sardine almost throughout the year, whereas microzooplankton was mostly dominant only during the October – December period. Coscinodiscus and Tintinids were predominant in the gut of Indian mackerel throughout the year. Furthermore, Thalassiosira, Ceratium, Dinophysis, Protoperidinium, Pyrophacus and copepods were also found in the gut of Indian mackerel almost throughout the year. The dominant value index showed the dominance of phytoplankton, microzooplankton and copepods in the diet of Indian mackerel throughout the year, indicating their almost equal preference for both phytoplankton and zooplankton. The food items in the gut content of Commerson’s anchovy showed characteristic difference from both Indian oil sardine and Indian mackerel and found to be a zooplankton feeder predominantly feeding on copepods, fish eggs, ostracods, lucifers and tintinids. The environmental observations based on monthly field sampling carried out in two locations (10m and 20m depth contours) situated off Kochi are presented. During seven out of nine observations, PFZ bands were observed around 10m location. High values of chlorophyll (> 3mg m-3) were found in August, September and October, which could be attributed to the combined effect of Cochin backwater influx and upwelling. The seasonal evolution of hydrographical parameters showed significantly higher concentration of nutrients and chlorophyll during the Southwest Monsoon period compared to the rest of the sampling. The chlorophyll concentration was found to be significantly higher in 10m location (PFZ) compared to the 20m location (non-PFZ). The status of the Length-Weight Relationship (LWR) and condition factor of Indian oil sardine, Indian mackerel and Commerson’s anchovy along the Kerala coast is presented. The LWR of Commerson’s anchovy is the very first detailed report from this region. LWR and condition factor of Indian mackerel and Oil sardine were not significantly different from the values reported in the historical studies, indicating that these parameters are not affected significantly by the expected long-term environmental changes. The results of the growth and maturity studies of the small pelagic fishes of interest have been discussed. The analyses were based on a fortnightly sampling carried out in two major landing centres during 2010 – 2011 periods. The maximum life span of Indian oil sardine was estimated to be 2.63 years. Two peaks of recruitment of juveniles to the fishery were observed; a large peak during July - August and a small peak in February - March. The length at first maturity was calculated as 15.7 cm while the length at first capture was 15 cm, suggesting that the peak exploitation of the species occurs before they attain sexual maturity. Comparison of the length at first maturity of oil sardine reported in historical studies with the present study shows that only minor variation exists between the two. The life span of Indian mackerel is estimated to be 2 years. The recruitment pattern showed the presence of mature mackerel all year round. However, two recruitment peaks of Indian mackerel were evident; June to August and February to March with the highest recruitment in July (28%). Probability of capture of mackerel showed higher values (22.43 cm) than the length at first maturity (17.7 cm) indicating that their peak exploitation occurs after attaining sexual maturity. Long-term changes in length at first maturity of Indian mackerel indicated a prominent decrease in length in the recent decade, probably indicating a response to the long-term environmental changes. The present study on the growth and maturity parameters of Commerson’s anchovy forms the first such study from Indian waters and the life span of the species was found to be 3.06 years. Two recruitment peaks of Commerson’s anchovy were observed; first during February – March and a second during June - July. The probability of capture of Commerson’s anchovy showed that they get exposed to maximum exploitation after they attain maturity. Lack of past data on length at first maturity of Commerson’s anchovy from the Indian coast hindered a possible comparison with the present data.

    Item Type: Thesis (Doctoral)
    Uncontrolled Keywords: major small pelagic fishes; Kerala Coast; Potential Fishery Zone; PFZ
    Subjects: Pelagic Fisheries
    Divisions: CMFRI-Kochi > Fishery Environment
    Subject Area > CMFRI > CMFRI-Kochi > Fishery Environment
    CMFRI-Kochi > Fishery Environment
    Subject Area > CMFRI-Kochi > Fishery Environment
    Depositing User: Arun Surendran
    Date Deposited: 25 Apr 2016 09:26
    Last Modified: 18 Jan 2017 08:52

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