Cheng-Hsin Liao

On the relationship between El Niño/Southern oscillation and South Pacific albacore

The influence of El Nino/Southern oscillation (ENSO) episodes on South Pacific albacore (Thunnus alalunga) is analyzed using historical catch per unit effort (CPUE) data collected from the Taiwanese distant-water longline fishing fleet, Southern oscillation indices and large scale measurements of seawater temperature. Two effects were identified from a time series analysis: (1) relatively low CPUE followed the onset of ENSO episodes with 8 and 4 yr time lag in fishing grounds between 10°S and 30°S and south of 30°S, respectively; and (2) towards the beginning of ENSO episodes CPUE was slightly higher in fishing grounds between the equator and 10°S. The time lag of the first effect corresponds to the time intervals that would be expected before the recruitment for the fish spawned during ENSO episodes. The second effect is interpreted as a result of the anomalous temperature structure of the seawater. The rise of the mixed layer depth (MLD) in the equatorial region as well as the narrowing volume of water comprising the albacores temperature preference in the subtropical region would both be expected to lead to a (slight) increase in the hook rate of albacore in the two regions.

Typhoon-enhanced upwelling and its influence on fishing activities in the southern East China Sea

Ocean–atmosphere interactions before and after the passage of Typhoons Haitang, Fung-wong, and Morakot across the southern region of the East China Sea (ECS) were examined by assessing satellite measurements of sea surface temperature (SST) and chlorophyll-a (chl-a) concentration in conjunction with wind data. In terms of the satellite-derived data, the SST declined and chl-a concentration increased after the passage of the typhoons, and this could have resulted from the upwelling induced by typhoons via their long-duration, strong winds. According to fisheries data collected after the passing of Typhoon Morakot, the major fishing grounds of the torchlight fishery were found to have shifted northwards from the northern tip of Taiwan to the southern ECS. Moreover, the major target fish species changed from skipjack tuna (pre-typhoon) to squid (post-typhoon), signifying that the typhoon-enhanced upwelling might have caused the skipjack tuna, which typically prefer warm water, to have migrated elsewhere. In contrast, the nutrient-rich, upwelled water might have directly led to increases in chl-a concentrations and contributed the increase in local squid densities. This study suggests that typhoons can cause marked cooling of the sea surface as well as enhance upwelling that previously resulted in not only chl-a increases but also changes of local fish communities and, consequently, fishing activities.

The Temporal and Spatial Change in Position of Squid Fishing Ground in Relation to Oceanic Features in the Northeastern Waters of Taiwan

We studied the squid fishing ground and satellite imageries of the northeastern waters of Taiwan, southern East China Sea, during the period of 1998-2001. Two obvious oceanic features, offshore thermal front and upwelling eddy that varied seasonally, were examined by using image edge detection function. The nearest distance of offshore thermal (or chlorophyll) front away from the coastline of Mainland China and the upwelling size (standard deviation) were generally within the range of 92 to 259 km and 643 to 2920 km^2, respectively. The monthly CPUEs and the spatial fishing position of torch-lighted squid fishery by season were varied with time. The CPUE was positively related with both the nearest distance of offshore thermal front to Mainland China and the size of upwelling eddy. In spring and summer, the fishing grounds were simultaneously formed in the shelf and coastal waters in the southern East China Sea. Its position was also anomaly varied and moved northward to the periphery of the upwelling during summer, as the upwelling was enhanced by passing typhoons. In autumn, the fishing ground was significantly formed further south in the vicinity of upwelling. Our result showed that location of the squid fishing ground was associated not only with oceanographic conditions of an extended area influenced by the Kuroshio, but also with local and instantaneous oceanographic environments (such as typhoon) in the southern East China Sea.

Effects of changes in sea surface temperature on fluctuation in larval anchovy resources in coastal waters of Taiwan

Monthly CPUEs of larval anchovies and monthly sea surface temperature anomalies (SSTA) from 1981 to 1999 were analyzed with the spectral analysis and the harmonic function analyses for the northeastern and southwestern coastal waters of Taiwan. The results showed that f or 3.4- and 4.6-year cycles, CPUEs fluctuated with SSTA in the opposite phase in the southwest coastal waters, but had in-phase fluctuation in the northeast coastal waters. The autumn fishing season in the northeast waters had higher catch than that of the spring fishing season, with the Encrasicholina as the main species. In the southwest coastal waters, however, the catch in the spring fishing season was higher than that of the autumn fishing season, with the Engraulis japonicus as the main species. The Engraulis japonicus is a cold-water species, migrating with the China Coastal Current, whereas the Encrasicholina is a warm-water species migrating with the Kuroshio Current. CPUE and SSTA showed different phases in fluctuation between the two fishing grounds. Since 1990, Engraulis japonicus catch decreased while Encrasicholina increased in the southwest region.

Impacts of Typhoons on Nutrient Supply and Potential Fish Production in the Southern East China Sea

Each year, typhoons (also called tropical cyclones or hurricanes) cause billions in property damage and great human toll. Besides, many typhoons occurring in tropical regions of the open ocean and their collective effects upon the marine environment and fishery remain undefined because of sampling difficulties. Recent satellite observations have shown that phytoplankton biomass can be enhanced for several days after typhoons, while in situ hydrographic observations, and data on biogeochemical properties and potential fish production induced by typhoons are limited. In this chapter, field observations are used to evaluate possible impacts of different typhoons on nutrient supply and potential fish production in the Southern East China Sea (SECS). The results provide evidence that typhoons add significantly to the nutrient supply and biological productivity in the SECS. The specific highlights are: (1) the typhoon-induced nitrate supplies after typhoons Fungwong (8.2 × 109 g N d−1) and Morakot (1.3 × 1010 g N d−1) are roughly 10-fold higher than that (1 × 109 g N d−1) during non-typhoon periods, and (2) the field observations demonstrate that typhoons can have a profound influence on nutrient supply and potential fish food sources in marginal seas.

Reproductive Biology of the Yellow Seabream (Dentex tumifrons ) in the Northern Waters off Taiwan

Reproductive biology of the yellow seabream (Dentex tumifrons) was described based on 1,400 specimens caught by otter trawlers in the northern waters off Taiwan and landed at Jinshan, Rueifang, and Dasi fishing ports from August 2005 to August 2006. Macroscopic appearance of the ovary, gonadosomatic index, and histological examination suggested that the yellow seabream spawns asynchronously, and spawning peaks in April and October, in the northern waters off Taiwan. Eight stages of oocyte development were determined based on histological examination, and ovarian development can be divided into immature, early maturing, late maturing and matured stages. The sex ratio of 0.704 was significantly different from 0.5 using χ2 test and decreased in compliance with the increasing of fork length in bigger specimens. The relationship between fecundity (F) and gonad weight (GW) was estimated to be F = 11.56 GW + 8.0745 (n = 25, P ＜ 0.05). Mean fecundity (± standard deviation) was estimated at 50151 ± 30379 eggs. Size of fork length (FL) at 50% maturity estimated by using the Logistic model was 154.8 mm and 168.6 mm for females and males, respectively.

Fishing Capacity and Conditions of Light Fishery under Different Fishing Light Intensity

A total of 116 nets of halogen light fishing under 6 classes of light intensity were conducted in the northern waters of Taiwan during June 19 to October 28, 2003. The average CPUE of 6 classes of light intensity showed that the CPUE was increased by the increasing intensity of fishing light and reached a peak under 80 kw condition. Cluster analysis indicated that the species composition from the 116 fishing nets could be divided into five major groups-A (squid group), B (hair-tail fish group), C (squid and hair-tail fish mixed group), D (file fish group), and E (multi-species group). The relationship between CPUE and light intensity was quite different in each group, probably due to the different species composition under different light intensity. In group A, the average CPUE of squid was not increased by increasing intensity of fishing light, it had the higher fishing capacity under 20 kw and 80 kw. In groups B and D, the average CPUE was increased by increasing intensity of fishing light. In group C, the average CPUE of hair-tail fish was also increased by increasing intensity of fishing light, but the average CPUE of squid was decreased by increasing intensity of fishing light, probably due to the aggregation of squid was discouraged by the presence of more hair-tail fish, a predator of squid, under higher light intensity. In group E, there is no relationship between CPUE and light intensity, due to the complexity in its species composition. Compared with the distribution of dorsal mantle length (ML) of squid, which was the major target spices of light fishery in Taiwan, we found that the smaller squid (ML＜ 80 mm) had higher CPUE at lower fishing light intensity (below 40 kw) than at higher intensity (above 60 kw). Conversely, for the larger squid (ML ＞80 mm), CPUE is better at higher capability of fishing light intensity. This result suggested that the CPUE of squid was influenced not only by the physical factor (capability of fishing light), but also by the biological factor such as body size, presence of predator, and so on.