Wang and Heino: Growth and maturation of Trichiurus japonicus in the subtropical Pacific Ocean 
173 
MODIS average SST (°C) in Dec-Feb 
MODIS averageSST (°C) in Jun-Aug 
Figure 1 
Map showing locations of the ports Kengfang and Tsukuan (black squares) in Taiwan where catch of 
the cutlassfish Trichiurus japonicus was sampled during 2013-2015 and locations of areas fished by the 
boats based at the 2 ports (open red triangles), with average summer (June-August) and winter (De- 
cember-February) sea-surface temperatures (SSTs in °C) around Taiwan. The SSTs are based on Moder¬ 
ate-resolution Imaging Spectroradiometer (MODIS) monthly mean SSTs for 2003-2014 (NASA Goddard 
Space Flight Center, Sea-viewing Wide Field-of-view Sensor [SeaWiFS] Ocean Color Data, website). 
Materials and methods 
Sampling 
We collected immature and adult cutlassfish, including 
the T. japonicus, from the pair-trawler fisheries month¬ 
ly at 2 fishing ports during 2013-2015: Kengfang (also 
transliterated as Gengfang) on the NE coast and Tsu¬ 
kuan (or Ziguan) on the SW coast of Taiwan (Fig. 1). 
The size of fishing boats (about 40 metric tons) and the 
fishing methods were similar during our sampling in 
these areas; for example, the nets had an array of mesh 
sizes descending from the opening to the codend (mini¬ 
mum mesh size: 2.0-2.5 cm), and the fishing depths 
were 100-150 m on the NE coast and 100-200 m on the 
SW coast (senior author, unpubl. data). The trawlers 
operate year-round along both coasts. However, fish¬ 
ing seasons for cutlassfishes varied: the fisheries along 
the NE coast catch cutlassfishes year-round, and the 
fisheries along the SW coast catch cutlassfishes mainly 
during autumn and early spring (September-February) 
and catch less in other months. Despite the differences 
in monthly distribution of catch between the areas, we 
attempted to collect samples evenly across months in 
both areas (Suppl. Table 1) (online only). Using a strati¬ 
fied random sampling design, we classified fish into 5 
size categories based on body depth (defined as the ver¬ 
tical distance between the dorsal margin of the body 
and the anus, in millimeters): mini (<20 mm), small 
(20-25 mm), medium (25-45 mm), large (45-70 mm), 
and extra large (>70 mm). For each sampling trip, we 
randomly collected 10-20 fish for each of the small, 
medium, and large size categories. Fish small or large 
enough to fall in the mini and extra-large categories 
were rarely found in the catch; however, we collected 
these animals when they were available. 
Despite the use of a standardized sampling scheme, 
maximum lengths and length distributions of samples 
of T. japonicus varied between the 2 areas. Maximum 
pre-anal lengths (i.e., the distance between the tip of 
upper jaw and the anterior side of anus) were 752 and 
379 mm for the T. japonicus landed in Kengfang (NE) 
and Tsukuan (SW), respectively (Fig. 2). Also, mean 
pre-anal lengths were generally smaller in Tsukuan 
than in Kengfang in each year and all 3 years com¬ 
bined (Suppl. Table 2) (online only). Distributions of sam¬ 
ple lengths were right-skewed in Kengfang but were 
approximately normal in Tsukuan (Fig. 2). We conduct¬ 
ed additional sampling in Tsukuan to obtain large T. 
japonicus specimens, but we could not find comparable 
samples. Therefore, the differences in length distribu¬ 
tions between areas probably were real and not due to 
sampling bias. 
Because of the presence of multiple cutlassfish spe¬ 
cies in the catch of trawlers, we identified the species 
that composed each sample on the basis of genetic 
analysis; the detailed methods and results of this anal¬ 
ysis have been published in Wang et al. (2017). For the 
subsequent analysis described here, we used only the 
specimens confirmed to be T. japonicus. 
Biological measurements 
We measured total length, pre-anal length, body depth, 
total weight, gonad weight, sex, and maturity state for 
individual fish. Because tail loss was common among 
the sampled fish, we used pre-anal length data to con¬ 
duct the analysis. We determined sex and maturity 
