Trends in abundance of marine fishery resources in India examined through dynamic factor analysis

Dynamic factor analysis (DFA) was used to identify common trends to explain the variability for a historical time series data (1980-2010) on all India annual marine fish landings for 16 resource groups. In this study, three common trends were identified for classifying the resource groups. Trend-1 increases gradually and reaches a peak in 1997, decreases sharply until 2001 and then increases further. Landings of carangids were clearly related to trend-1 with positive factor loading magnitude. Trend-1 is important for Bombayduck as well but with negative factor loading. In the case of trend-2, it is declining until 1993 and remains steady with slight fluctuations till 2003 and increases further. Both, silverbellies and pomfrets landings were determined by trend-2 with similar positive factor loadings. All other resources were associated with more than one trend. Trend-3 shows an increasing trend throughout the period with slight fluctuations. Perches, seerfishes, tunnies, flatfishes, crustaceans and molluscs formed a homogenous group associated with both trend-1 and trend-3. These trends were important for elasmobranchs too as they had similar loadings on both trends but with opposite signs. Resource-wise explanations based on the different trends are discussed citing the examples of clupeids, carangids, Bombayduck, pomfrets and silverbellies