The influence of chlorophyll-a and sea surface temperature on anchovy catch trends (2011-2024) in Kilwa, Tanzania

Anchovies exhibit varying trends in catch worldwide, with some regions experiencing declines in catch due to overfishing and environmental changes, while others remain stable or experience increases. Kilwa is among the most productive small pelagic fisheries along the Tanzanian coast. This study aimed to investigate the influence of Chlorophyll-a (Chl-a) and Sea Surface Temperature (SST) on anchovy catch trends in Kilwa. The study further examined the relationship between catch per unit effort (CPUE) and total anchovy catch, as well as its implications for fisheries management. The study was conducted at two sites: Kilwa Kivinje and Kilwa Masoko during both the northern eastern monsoon (high season) and the southern eastern monsoon (low season). The results revealed that catch at Kilwa Kivinje increased from 95,982 kg year-1 in 2011 to 123,754 kg year-1 in 2024. Whereas, at Kilwa Masoko, the catch increased from 63,988 kg year-1 in 2011 to 89,994 kg year-1 in 2024. Catches were consistently higher in Kilwa Kivinje than in Kilwa Masoko and peaked during the high season (Fisher’s PLSD; p < 0.0031). The catch was composed of four species: Encrasicholina devisi, Encrasicholina punctifer, Encrasicholina heteroloba, and Stolephorus commersonnii which was the least dominant in the catches. Furthermore, results indicated that anchovy catches were positively linked to Chl-a levels [(R2 = 0.763, t = 6.215, p < 0.0001) Kilwa Masoko, (R2 = 0.597, t = 4.215, p < 0.012) Kilwa Kivinje], but negatively to SST (R2 = 0.179, t = -1.618, p < 0.1316) Kilwa Kivinje, (R2 = 0.349, t = -2.536, p < 0.0261) Kilwa Masoko. Additionally, CPUE correlated positively with total catch, indicating that overfishing remains a concern, as increasing effort beyond sustainable limits can lead to stock depletion. These results highlight the need for effective fisheries management to optimize fishing effort while ensuring long-term sustainability in Kilwa.