Chinese Journal of Oceanology and Limnology   2017, Vol. 35 issue(4): 902-911     PDF       
http://dx.doi.org/10.1007/s00343-017-6115-4
Institute of Oceanology, Chinese Academy of Sciences
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Article Information

WANG Xuehui(王雪辉), QIU Yongsong(邱永松), ZHANG Peng(张鹏), DU Feiyan(杜飞雁)
Natural mortality estimation and rational exploitation of purpleback flying squid Sthenoteuthis oualaniensis in the southern South China Sea
Chinese Journal of Oceanology and Limnology, 35(4): 902-911
http://dx.doi.org/10.1007/s00343-017-6115-4

Article History

Received Apr. 20, 2016
accepted in principle Jun. 12, 2016
accepted for publication Jun. 27, 2016
Natural mortality estimation and rational exploitation of purpleback flying squid Sthenoteuthis oualaniensis in the southern South China Sea
WANG Xuehui(王雪辉), QIU Yongsong(邱永松), ZHANG Peng(张鹏), DU Feiyan(杜飞雁)        
Guangdong Provincial Key Laboratory of Fishery Ecology and Environment, South China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou 510300, China
ABSTRACT: Based on the biological data of purpleback flying squid (Sthenoteuthis oualaniensis) collected by light falling-net in the southern South China Sea (SCS) during September to October 2012 and March to April 2013, growth and mortality of 'Medium' and 'Dwarf' forms of squid are derived using the Powell-Wetherall, ELEFAN methods and length-converted catch curves (FiSAT package). Given a lack of commercial exploitation, we assume total mortality to be due entirely to natural mortality. We estimate these squid have fast growth, with growth coefficients (k) ranging from 1.42 to 2.39, and high natural mortality (M), with estimates ranging from 1.61 to 2.92. To sustainably exploit these squid stocks, yield per recruitment based on growth and natural mortality was determined using the Beverton-Holt dynamic pool model. We demonstrate squid stocks could sustain high fishing mortality and low ages at first capture, with an optimal fishing mortality >3.0, with the optimal age at first capture increased to 0.4-0.6 years when fishing mortality approached optimal levels. On the basis of our analyses and estimates of stock biomass, we believe considerable potential exists to expand the squid fishery into the open SCS, relieving fishing pressure on coastal waters.
Key words: purpleback flying squid     Sthenoteuthis oualaniensis     mortality     dynamic pool model     fishery     South China Sea    
1 INTRODUCTION

The oceanic purpleback flying squid Sthenoteuthis oualaniensis (Lesson, 1830) is widely distributed throughout tropical and subtropical waters of the Indo-Pacific. It is considered to be the most abundant large squid of commercial importance in the region (Dunning, 1998). Whereas commercial fisheries have targeted this species in the Pacific and Indian Oceans, in the South China Sea (SCS) fisheries have hardly developed (Zhang et al., 2010). The species is widely distributed in the open SCS, with an estimated standing biomass of (1.10-2.30)×106 tons (Siriraksophon et al., 2001; Zhang, 2005; Zhang et al., 2014, 2015a). Accordingly, there is considerable potential for development of a fishery for this species (Zhang et al., 2010; Qiu et al., 2014).

From a fisheries perspective the biology of purpleback flying squid in the SCS has been little studied (Fan et al., 2013). Two morphologically distinct forms (phenogroups) of this species occur here: a 'medium' and a 'dwarf' form. The 'medium' form is larger and possesses a dorsal photophore, whereas the smaller 'dwarf' lacks this dorsal photophore (Nesis, 1993). These two forms are also genetically (Li et al., 2014) and morphologically (Fan et al., 2015; Jiang et al., 2015; Zhu et al., 2016) distinct. Feeding and reproduction in this species (without differentiating forms) have also been described in waters around the Nansha and Xisha Islands in the SCS (Yan et al., 2012; Zhang et al., 2013). Some biological information, such as sex ratios and sexual maturity of these two forms, has also been recently detailed (Zhang et al., 2015b).

Interest in developing a fishery for purpleback flying squid in the open SCS has grown because of overfishing in coastal waters (Lymer et al., 2010; Qiu et al., 2010; Zhang et al., 2010; Qiu et al., 2014). To best develop this fishery, stock assessment models (such as a dynamic pool model) must be established, for which determining natural mortality—that mortality due to all causes other than fishing—is essential. There are indirect ways of estimating this using growth parameters, but most (and perhaps all) are little more than 'guesstimates' or 'qualified' guesses (Sparre and Venema, 1998). The near complete absence of exploitation of this species provides an opportunity to estimate its natural mortality.

Using samples of purpleback flying squid collected in the southern SCS, we estimated mantle lengthweight relationships, and growth and mortality parameters of females and males, 'medium' and 'dwarf' forms using FiSAT (FAO-ICLARM Stock Assessment Tools; Gayanilo et al., 2005). Lengthconverted catch curves are used to derive total mortality (Z), with natural mortality (M) assumed to equal total mortality (Z) given the effects of fishing mortality are negligible or non-existent. We also determine the optimal ages/mantle lengths at first capture, and fishing mortality rates using the Beverton-Holt dynamic pool model (Beverton and Holt, 1957). Our results contribute to a better understanding of the fisheries biology of S. oualaniensis, and if heeded, we believe will also contribute to its more sustainable management and exploitation as a fisheries resource.

2 MATERIAL AND METHOD 2.1 Data collection

Purpleback flying squid were collected from the southern SCS during fisheries surveys using a light falling-net between September and October 2012 and between March and April 2013 (Table 1 and Fig. 1). The vessel, FV Guibeiyu 96886, has a main engine power of 382 kW, overall length of 41.80 m, and gross tonnage of 413 tons. This vessel has 230 attracting lamps (1 kW/lamp) along either side, and a net of 281.60 m circumference, 80.18 m stretched length, cod-end mesh of 22 mm, and mesh at the net mouth of 52 mm, for which the maximum working depth was 50 m.

Table 1 Sampling period, area and sample size
Figure 1 Southern SCS survey locations

In the event less than 50 purpleback flying squid were captured in any given haul, all specimens were retained for study; 50 random squid were otherwise collected. All squid were frozen immediately and returned to shore, where they were defrosted and measured in our laboratory. Squid were sorted into 'medium' (M) form (with), and 'dwarf' (D) form (without) a dorsal photophore, and then for each individual, its sex, mantle length (ML), wet weight (W), maturity stage, and stomach grade were recorded (with ML and W measured to the nearest 0.1 cm and 0.1 g, respectively) (Table 1).

2.2 Methods 2.2.1 Mantle length and weight relationships

Parameters 'a' and 'b' in the mantle length (ML) and weight (W) relationship, W=aMLb, were estimated from the intercept and slope of the linear regression on the log-transformed weight and ML data, i.e., log (W)=log(a)+blog(ML). Outliers were identified and excluded and the growth stanzas processed following the method of Wang et al. (2011). As samples were dominated by juveniles, we analyzed average values of mantle length and weight in 5-mm-length groups to balance weights of all size groups in regressions (Ricker, 1958). We judged the type of growth according to comparing the b values obtained from the exponential index of the ML-W relationship with the value 3 (Wang et al., 2012).

2.2.2 Growth and mortality parameters estimation

Growth of squid was simulated using the von Bertalanffy growth function (VBGF) (Sparre and Venema, 1998). The asymptotic mantle length (ML) and Z/k (Z=total mortality; k=growth coefficient) were estimated using the Powell-Wetherall method in the FiSAT package (Powell, 1979; Wetherall, 1986). Estimates were based on ML-frequency data from 2012-2013, using class intervals of 5 mm. The t0 is the constant of VBGF with the age at mantle length=0. We assumed t0=0 (Pauly, 1985; Jarre et al., 1991; Chembian, 2013).

Growth performance index (φ) was computed using the following equation (Pauly and Munro, 1984):

We used a length-converted catch curve to estimate total mortality Z (Pauly, 1983, 1984a, 1984b) and in the near absence of commercial catch assumed total mortality (Z) was due entirely to natural mortality (M) (Zhang, 2005; Zhang et al., 2010), i.e., Z=M.

For comparison, rates of natural mortality were also estimated by empirical formulas used for squid (Pauly, 1980, 1985; Srinath, 1991; Jensen, 1996; Mohamed, 1996; Nevárez-Martínez et al., 2006; Chembian, 2013):

(Pauly, 1980, 1985; Chembian, 2013),

M2 =0.4603+1.4753k (Srinath, 1991; Mohamed, 1996),

and

M3 =1.5k (Jensen, 1996; Nevárez-Martínez et al., 2006),

where M1, M2 and M3 are the natural mortality rates calculated using the different empirical formulas, W is the asymptotic body weight, k is the VBGF parameter, and T is the mean environmental temperature. For T we used recent 5-year-averaged annual sea surface temperature (SST) data for the southern SCS (5°-16°N, 109°-117°E) from NOAA Extended Reconstructed SST (http://www.ncdc.noaa.gov/oa/climate/research/sst/sst.html), which is 28.6 ℃.

2.2.3 Dynamic pool model

The yield per recruitment (Yw/R) calculated by the Beverton-Holt model (Beverton and Holt, 1957) was used to assess the optimal status of exploitation for the squid stocks. The Yw/R was derived by resolving the integration of the equation:

where F is the fishing mortality rate, W is the asymptotic body weight, M is the natural mortality rate, tc is the age at first capture, tr is the age at recruitment, k and t0 are von Bertalanffy growth parameters, and b is the exponential index of the mantle length-weight relationship.

The integration was conducted over the ages from tc to the presumed asymptotic age of 2. This presumed asymptotic age was based on reported ages of about 1 year for oceanic purpleback flying squid in the northwestern Indian Ocean (Chen et al., 2007), and the fact that using a larger asymptotic age would have very limited influence on Yw/R values.

3 RESULT 3.1 Mantle length and weight relationships

The regression curves of ML and weight relationships for purpleback flying squid are shown in Fig. 2. All coefficients of determination (R2) are >0.99 (Table 2). The b values vary from 2.933 to 3.556 with a mean of 3.216±0.126. The t-tests indicate that the 'medium' form of this species has a positive allometric growth and the 'dwarf' form has an isometric growth. The ML and weight regression curves of the 'medium' form differ significantly from the 'dwarf' form (F=74.70 for females and males combined, F=73.89 for females, F=72.77 for males, P < 0.001 for all).

Figure 2 Regression curves of ML and body weight of southern SCS purpleback flying squid a: ♀ and ♂ combined; b: ♂; c: ♀.
Table 2 Relationships between mantle length and weight of southern SCS purpleback flying squid
3.2 Growth parameters

Mantle length frequencies and growth curves simulated by ELEFAN I are depicted in Fig. 3. Growth parameters (ML and k) derived from length frequency data using Powell-Wetherall technology of FiSAT package and the growth performance index (φ) are listed in Table 3. The ages at first recruitment (tr) were determined from the first modes of length frequencies and calculated using the VBGF. The results revealed distinct differences in growth parameters between 'medium' and 'dwarf' forms, with the size and growth rate of the former greater than the latter.

Figure 3 Purpleback flying squid ML frequency and growth curves estimated by ELEFAN I a: M ♀; b: M ♂; c: D ♀; d: D ♂.
Table 3 Growth and mortality of southern SCS purpleback flying squid
3.3 Mortality rate

Total mortality (Z) parameters estimated using the length-converted catch curves are shown in Fig. 4. When data were selected for regression analysis, the first and last data points were removed; the first data points represent squid that have yet to enter the recruitment period, and the last represent squid whose sizes are close to the asymptotic size. The slopes for b obtained from linear regressions corresponding to Z are listed in Table 3. For comparison, we calculated the natural mortality rates using other empirical formulas (Table 4). The results demonstrate mean values of natural mortality rates for purpleback flying squid range from 2.23 to 3.45, with 'medium' form squids having higher natural mortality rates.

Figure 4 Estimated total mortality from length-converted catch curves a. M ♀; b. M ♂; c. D ♀; d. D ♂.
Table 4 Estimates of natural mortality in purpleback flying squid using different methods
3.4 Dynamic pool model

Yield per recruitment (Yw/R) was calculated using dynamic pool models with inputs of growth, natural mortality and age-at-recruitment parameters (Table 3), and isoline plots derived from the values of Yw/R (Fig. 5). The dash lines indicate the present status of ages/mantle lengths at first capture. Because of high growth and high natural mortality rates, the four plots demonstrate squid stocks could sustain fishing mortality rates as high as >3.0 and early ages at first capture of about 0.5 years. If fishing mortality rates were to be increased to approach optimal levels, the current ages/mantle lengths at first capture for all four stocks have to be increased (Table 5).

Figure 5 The Yw/R in relation to fishing mortality (F) and age (tc)/mantle length (MLc) at first capture Dashed lines represent the present ages/mantle lengths at first capture; solid lines represent the optimal ages/mantle lengths at first capture when fishing mortality approach the optimal levels; the Yw/R values for combinations of fishing mortality and age/mantle length at first capture are listed in Table 5.
Table 5 The Yw/R calculated for combinations of fishing mortality and age/mantle length at first capture of southern SCS purpleback flying squid
4 DISCUSSION 4.1 Mantle length-weight relationships

The use of mantle length-weight relationships should be limited to the nekton sizes used for estimating the associated parameters: it is inaccurate to extrapolate data to juvenile and immature stages (Ricker, 1975). Therefore, when data are regressed for a mantle lengthweight relationship, samples should include evenly represented size ranges of squid. As juveniles dominated our samples, we had to reduce their influence on regressions, so analyses were applied to average values of mantle length and weight for length groups.

Morphometrics have been used to resolve systematic ambiguities to differentiate species (Cohen, 1976; Evans, 1976). Our scatter plots of mantle length and weight reveal differences in growth trends between the 'medium' and 'dwarf' purpleback squid forms. The t-tests of b indicate that 'medium' females and males have positive allometric growth, whereas 'dwarf' females and males have an isometric growth. The b values regressed for the 'medium' form were also greater than those for the 'dwarf' form (Table 2), which are similar to those observed in the Hawaiian waters and in the southwest coast of India (Suzuki et al., 1986; Chembian and Mathew, 2014). Differences in forms of purpleback flying squid have now been confirmed by the gene sequences (Li et al., 2014), the presence or absence of a dorsal photophore (Nesis, 1993), and morphometric studies (Fan et al., 2015; Jiang et al., 2015; Zhu et al., 2016), to which we can now add differences in mantle length-weight relationships.

4.2 Growth and mortality rate

Based on ML frequency, our analyses provide the first estimates of growth parameters for purplebackfl ying squid in the SCS. The growth coefficients (k) estimated using the FiSAT package are high, ranging from 1.42/year to 2.39/year. Previous studies using statoliths have demonstrated similar high growth rates for this species outside the SCS (Nesis, 1977; Zuyev et al., 2002; Chen et al., 2007). It has been suggested that the growth performance index (φ) could be used to compare the growth of fish and invertebrates (Pauly and Munro, 1984). As we know of no previous study on growth of S. oualaniensis in the SCS, we can only compare our φ estimates of 2.34-3.22 with those for the same species from outside this region. Growth performance indexes have been reported from between 3.04 and 3.12 for purpleback flying squid and 2.58 and 3.28 for Uroteuthis duvaucelii (d'Orbigny, 1835) in Indian coastal waters (Mohamed, 1996; Chembian, 2013 (as Loligo duvaucelii)). Therefore, growth performance indexes of purpleback flying squid in the SCS are slightly below those of this species in Indian waters, and similar to those of U. duvaucelii.

Given the near absence of historical commercial exploitation of purpleback flying squid in the SCS, natural mortality (M) was estimated as M=Z. The total standing biomass of this squid in the SCS was estimated to be (1.4-2)×106 tons (Siriraksophon et al., 2001; Zhang, 2005), but the actual fishery catch was small—a total landing less than 5×104 tons (Zhang et al., 2010). Given the actual catch (C) and average standing biomass (B), we estimate fishing mortality rates (F=C/B) of 0.025-0.036, which are negligible compared with estimated natural mortality rates (1.61-2.92). Therefore, we can assume that the total mortality Z is entirely due to natural mortality M.

Mortality rate estimates for purpleback flying squid have not been previously reported for the SCS. We recognize them to be high. Ehrhardt et al. (1983) inferred squid mortality rates must be quite high given the typically short lifespans of squid, their intermediary trophic levels, and the marked frequency of cannibalism. Additionally, purpleback flying squid are tropical-subtropical in distribution, and tropical species have higher mortality rates than colder-water species. Our estimates based on growth parameters and environmental temperature (Table 4) also support the high mortality rates derived from length-converted catch curves.

4.3 Optimal exploitation

Table 5 presents yield per recruitment (Yw/R) values for various combinations of ages/sizes at first capture and fishing mortality for purpleback flying squid. The current sizes at first capture are acceptable under current low fishing mortality, because they produce a higher Yw/R. However, if fishing mortality were to approach the optimal level in any future fishery, size at first capture, especially of female 'medium' form squid, has to be increased. The proportion of 'medium' to 'dwarf' form squid in the total squid catch is 88.9% and 11.1%, respectively (Zhang et al., 2015b), with the 'medium' form squid biomass accounting for 97.2% of the total catch weight. Therefore, increasing the sizes at first capture of all squid stocks would correspond to an increase in the overall Yw/R. However, under the current low fishing mortality, if the sizes at first capture remained constant and fishing mortality increased to >3.0, then the Yw/R values for both squid 'forms' would be greatly increased, indicating stocks were being underexploited. Zhang et al. (2015b) studied maturity of purpleback flying squid in the SCS and indicated that mantle lengths at first maturity for 'medium' form females and males were 18.0 cm and 12.6 cm, respectively; and those for 'dwarf' form females and males were 9.5 cm and 8.1 cm, respectively. Based on the sizes at first capture for optimal fishing in the present study and the sizes at first maturity from Zhang et al. (2015b), we suggest the sizes at first capture after first maturity should be 18.0 cm and 12.6 cm for 'medium' form females and males, and 9.5 cm and 8.6 cm for 'dwarf' form females and males.

Zhang et al. (2014) estimated stock size of purpleback flying squid using a scientific echosounder in the SCS and determined the total standing biomass to be > 2.00×106 tons. Given the total landing of < 50 000 tons by neighboring countries (Zhang et al., 2010) and the abundant standing biomass, there is considerable potential for greater exploitation of squid stocks in the open SCS. Southern and southeastern Asian countries have policies to expand exploitation of open-sea fishery resources (Lymer et al., 2010), as does China (Qiu et al., 2014). In some cases, policy states that moving offshore is to transfer fishing pressure from overfished inshore regions to underexploited offshore regions. As oceanic purpleback flying squid have to date been minimally exploited, and they are short-lived, characterized by fast growth with year-round spawning strategy (Chen et al., 2008), their exploitation would certainly reduce fishing pressure in coastal waters. That said, any new resource exploitation will require a coordinated effort to ensure efficient and sustainable harvesting, processing and marketing of resources (Lymer et al., 2010). In this regard, our study provides fundamental information to enable sustainable exploitation of this abundant squid resource.

5 CONCLUSION

Based on the biological data of purpleback flying squid collected by light falling-net in southern SCS. We estimate these squid have fast growth, with growth coefficients (k) ranging from 1.42 to 2.39, and high natural mortality (M), with estimates ranging from 1.61 to 2.92. We demonstrate squid stocks could sustain high fishing mortality and low ages at first capture, with an optimal fishing mortality >3.0, with the optimal age at first capture increased to 0.4-0.6 years when fishing mortality approached optimal levels. On the basis of our analyses and estimates of stock biomass, we believe considerable potential exists to expand the squid fishery into the open SCS, relieving fishing pressure on coastal waters.

6 ACKNOWLEDGEMENT

We are grateful to Dr. CHEN Yong for his help to complete the manuscript. We thank CHEN Sen, LI Jie, YAN Lei and YANG Bingzhong for their assistance in sample and data collection, and WANG Lianggen and LI Zengguang for their help in preparing figures. We thank to two anonymous reviewers for their comments and suggestions on the manuscript.

References
Beverton R J H, Holt S J, 1957. On the Dynamics of Exploited Fish Populations. Her Majesty's Stationery Office, London.
Chembian A J, Mathew S, 2014. Population structure of the purpleback squid Sthenoteuthis oualaniensis (Lesson, 1830) along the south-west coast of India. Indian Journal of Fisheries, 61(3): 20–28.
Chembian A J. 2013. Studies on the biology, morphometrics and biochemical composition of the ommastrephid squid, Sthenoteuthis oualaniensis (Lesson, 1830) of the south west coast of India. Cochin University of Science and Technology.
Chen X J, Liu B L, Chen Y, 2008. A review of the development of Chinese distant-water squid jigging fisheries. Fisheries Research, 89(3): 211–221. Doi: 10.1016/j.fishres.2007.10.012
Chen X J, Liu B L, Tian S Q, Qian W G, Zhao X H, 2007. Fishery biology of purpleback squid, Sthenoteuthis oualaniensis, in the northwest Indian Ocean. Fisheries Research, 83(1): 98–104. Doi: 10.1016/j.fishres.2006.09.005
Cohen A C, 1976. The systematics and distribution of Loligo(Cephalopoda, Myopsida) in the western north Atlantic, with descriptions of two new species. Malacologia, 15(2): 299–367.
Dunning M C, 1998. A review of the systematics, distribution, and biology of the arrow squid genera Ommastrephes Orbigny, 1835, Sthenoteuthis Verrill, 1880, and Ornithoteuthis Okada, 1927 (Cephalopoda:Ommastrephidae). Smithson. Contrib. Zool., 586: 425–433.
Ehrhardt N M, Jacquemin P S, Garcia B F, Gonzalez D G, Lopez B J M, Ortiz C J, Solius N A. 1983. On the fishery and biology of the giant squid Dosidicus gigas in the Gulf of California, Mexico. In: Advances in Assessment of World Cephalopod Resources. FAO, Rome. p. 306-340.
Evans R G, 1976. Aspects of the Population Biology of the California Market Squid (Loligo opalescens, Berry). California State University, Hayward, CA.
Fan J T, Feng X, Qiu Y S, Huang Z R, Chen G B, 2013. Review on the biology of purpleback flying squid in South China Sea. Guangdong Agricultural Science, 40(23): 122–128.
Fan J T, Qiu Y S, Chen Z Z, Feng X, Zhang J, 2015. Morphological difference of the beak between two stocks of Sthenoteuthis oualaniensis inhabiting South China Sea. Periodical of Ocean University of China, 45(10): 42–59.
Gayanilo F C Jr, Sparre P, Pauly D. 2005. FAO-ICLARM Stock Assessment Tools Ⅱ (FiSA Ⅱ). User's guide. FAO Computerized Information Series (Fisheries). No. 8, Revised version. FAO, Rome.
Jarre A, Clarke M R, Pauly D, 1991. Re-examination of growth estimates in oceanic squids:the case of Kondakovia longimana (Onychoteuthidae). ICES J. Mar. Sci., 48(2): 195–200. Doi: 10.1093/icesjms/48.2.195
Jensen A L, 1996. Beverton and Holt life history invariants result from optimal trade-off of reproduction and survival. Can. J. Fish. Aquat. Sci., 53(4): 820–822. Doi: 10.1139/f95-233
Jiang Y E, Zhang P, Lin Z J, Qiu Y S, Fang Z Q, Chen Z Z, 2015. Statolith morphology of purpleback flying squid(Sthenoeuthis oualaniensis) in the offshore South China Sea. South China Fisheries Science, 11(5): 27–37.
Li M, Zhang P, Chen Z Z. 2014. Genetic differentiation between medium form and dwarf form of Sthenoteuthis oualaniensis in the South China Sea. In: Annual conference of China Society of Fisheries. p. 321. (in Chinese with English abstract)
Lymer D, Funge-Smith S, Miao W, 2010. Status and potential of fisheries and aquaculture in Asia and the Pacific 2010. FAO Regional Office for Asia and the Pacific. RAP Publication, Bangkok.
Mohamed S K, 1996. Estimates of growth, mortality and stock of the Indian squid Loligo duvauceli Orbigny, exploited off Mangalore, southwest coast of India. Bulletin of Marine Science, 58(2): 393–403.
Nesis K N, 1977. Population structure in the squid Sthenoteuthis oualaniensis (Lesson, 1830) (Ommastrephidae) in the western tropical Pacific. Trudy Inst. Oceanol. Acad. Sci., 107: 15–29.
Nesis K N. 1993. Population structure of oceanic ommastrephids, with particular reference to Sthenoteuthis oualaniensis: a review. In: Okutani T, O'Dor R K, Kubodera T eds. Recent Advances in Cephalopod Fisheries Biology. Tokai University Press, Tokyo. p. 375-383.
Nevárez-Martínez M O, Méndez-Tenorio F J, Cervantes-Valle C, López-Martínez J, Anguiano-Carrasco M L, 2006. Growth, mortality, recruitment, and yield of the jumbo squid (Dosidicus gigas) off Guaymas, Mexico. Fisheries Research, 79(1-2): 38–47. Doi: 10.1016/j.fishres.2006.02.011
Pauly D, Munro J L, 1984. Once more on the comparison of growth in fish and invertebrates. Fishbyte, 2(1): 21.
Pauly D, 1980. On the interrelationships between natural mortality, growth parameters, and mean environmental temperature in 175 fish stocks. J. Cons. Int. Explor. Mer., 39(2): 175–192. Doi: 10.1093/icesjms/39.2.175
Pauly D, 1983. Length-converted catch curves:a powerful tool for fisheries research in the tropics (part 1). Fishbyte, 1(2): 9–13.
Pauly D, 1984a. Length-converted catch curves:a powerful tool for fisheries research in the tropics (part 2). Fishbyte, 2(1): 17–19.
Pauly D, 1984b. Length-converted catch curves:a powerful tool for fisheries research in the tropics (Ⅲ:conclusion). Fishbyte, 2(3): 9–10.
Pauly D, 1985. Population dynamics of short-lived species, with emphasis on squids. NAFO Sci. Coun. Studies(9): 143–154.
Powell D G, 1979. Estimation of mortality and growth parameters from the length frequency of a catch. Cons. Int. Explor. Mer., 175: 167–169.
Qiu Y S, Lin Z J, Wang Y Z, 2010. Responses of fish production to fishing and climate variability in the northern South China Sea. Progress in Oceanography, 85(3-4): 197–212. Doi: 10.1016/j.pocean.2010.02.011
Qiu Y, Zhang P, Xu Y. 2014. Suggestions for exploitation of oceanic pelagic fisheries resources in the South China Sea. In: The thirty-third Forum on Science and Technology in China. China Association for Science and Technology, Haikou, China. p. 1-6. (in Chinese)
Ricker W E, 1958. Handbook of Computations for Biological Statistics of Fish Populations. Fisheries Research Board of Canada, Ottawa300p.
Ricker W E, 1975. Computation and Interpretation of Biological Statistics of Fish Populations. Bulletin of the Fisheries Research Board of Canada, Ottawa382p.
Siriraksophon S, Nakamura Y, Sukramongkol N, 2001. Exploration of purpleback flying squid, Sthenoteuthis oualaniensis resources in the South China Sea. Southeast Asian Fisheries Development Center Training Department, Samutprakan, Thailand.
Sparre P, Venema S C. 1998. Introduction to tropical fish stock assessment. part 1. Manual. FAO Fisheries Technical Paper. No. 306. 1, Rev. 2. FAO, Rome.
Srinath M, 1991. Letters to the Editor. Fishbyte, 9(1): 1–2.
Suzuki T, Yamamoto S, Ishii K, Matsumoto W M, 1986. On the flying squid Stenoteuthis oualaniensis (Lesson) in Hawaiian waters. Bull. Fac. Fish. Hokkaido Univ., 37(2): 111–123.
Wang X H, Qiu Y S, Zhu G P, Du F Y, Lin Z J, Sun D R, Huang S L, 2012. Population parameters and dynamic pool models of commercial fishes in the Beibu Gulf, northern South China Sea. Chinese Journal of Oceanology and Limnology, 30(1): 105–117. Doi: 10.1007/s00343-012-1017-y
Wang X H, Qiu Y S, Zhu G P, Du F Y, Sun D R, Huang S L, 2011. Length-weight relationships of 69 fish species in the Beibu Gulf, northern South China Sea. Journal of Applied Ichthyology, 27(3): 959–961. Doi: 10.1111/j.1439-0426.2010.01624.x
Wetherall J A, 1986. A new method for estimating growth and mortality parameters from length-frequency data. Fishbyte, 4(1): 12–14.
Yan Y R, Feng B, Lu H S, Lai J Y, Du S Q, 2012. Fishery biology of purpleback flying squid Sthenoteuthis oualaniensis in northern sea areas around Nansha Islands in summer. Oceanologia et Limnologia Sinica, 43(6): 1177–1186.
Zhang J, Chen G B, Zhang P, Chen Z Z, Fan J T, 2014. Estimation of purpleback flying squid (Sthenoteuthis oualaniensis) resource in the central and southern South China Sea based on fisheries acoustics and light-falling net. Journal of Fishery Sciences of China, 21(4): 822–831.
Zhang J, Chen Z Z, Chen G B, Zhang P, Qiu Y S, Yao Z, 2015a. Hydroacoustic studies on the commercially important squid Sthenoteuthis oualaniensis in the South China Sea. Fisheries Research, 169: 45–51. Doi: 10.1016/j.fishres.2015.05.003
Zhang P, Yan L, Yang B Z, Tan Y G, Zhang X F, Chen S, Li J, 2015b. Population structure of purpleback flying squid(Sthenoteuthis oualaniensis) in Nansha area in spring. South China Fisheries Science, 11(5): 11–19.
Zhang P, Yang L, Zhang X F, Tang Y G, 2010. The present status and prospect on exploitation of tuna and squid fishery resources in South China Sea. South China Fisheries Science, 6(1): 68–74.
Zhang Y M, Yan Y R, Lu H S, Zheng Z W, Yi M R, 2013. Study on feeding and reproduction biology of purple flying squid, Sthenoteuthis oualaniensis in the western South China Sea. Journal of Guangdong Ocean University, 33(3): 56–64.
Zhang Y, 2005. Fisheries Acoustic Studies on the Purpleback Flying Squid Resource in the South China Sea. National Taiwan University, Taipei, China.
Zhu K, Wang X, Zhang P, Du F, Qiu Y. 2016. A study on morphological variations and discrimination of medium and dwarf forms of purple flying squid Sthenoteuthis oualaniensis in the southern South China Sea. Journal of Tropical Oceanography, in press. (in Chinese with English abstract)
Zuyev G, Nigmatullin C, Chesalin M, Nesis K, 2002. Main results of long-term worldwide studies on tropical nektonic oceanic squid genus Sthenoteuthis:an overview of the Soviet investigations. Bulletin of Marine Science, 71(2): 1019–1060.