Marine Biology (1994) 121:211-217
9 Springer-Verlag 1994
B. Morales-Nin
Growth of demersal fish species of the Mexican Pacific Ocean
Received: 10 December 1993 / Accepted: 4 August 1994
A b s t r a c t The growth of 24 species of demersal fish caught off the Sinaloa-Nayarit coast and in the Gulf of Tehuantepec (Mexican Pacific Ocean) was determined by means of length-frequency analysis. Fishes constitute an important bycatch of the penaeid shrimp fishery, and 235 species were identified in catches made on research cruises in both areas in 1989 to 1992. Growth rates (cm yr -1) ranged from 0.13 cm for lutjanids and serranids to 0.95 cm for the carangid Selene peruviana; the other species displayed growth rates within this range. Growth varied seasonally, with minimum growth in spring, and is probably related to seasonal changes in the waters of the area. By means of length-frequency analysis, we determined von Bertalanffy growth parameters for the primary species of this multispecies fishery. Such data is fundamental for the future commercial exploitation of these fishes.
Introduction Estimation of growth in tropical marine fish has long been problematic because of the supposed lack of annual rings in their hard structures (scales, otoliths and vertebrae). Moreover, their "continuous" spawning has been assumed to render impossible growth analysis based on length-frequency data (Mohr 1921). However, during the 1960s and 1970s, it was realized that tropical marine fish generate annual rings in their hard parts under a wide range of conditions. Also, it was found that growth could be estimated for many tropical fish stocks by analyzing seasonal growth rings within the otoliths (Poinsard and Troadec 1966; Longhurst and Pauly 1987; Morales-Nin 1989, 1992).
Communicated by J. M. Pdr~s, Marseille B. Morales-Nin CSIC-Institut d'Estudis Avangats de les Illes Balears, Crta. Valldemossa Km 7.5, E-07071 Palma de Mallorca, Spain
While spawning in tropical fish is often more prolonged than in their temperate fellows, it is usually concentrated in one or two periods each year. Changes in fish spawning are only partially responsible for recruitment fluctuations. The occurrence of recruitment windows during larval and juvenile stages (Bakun et al. 1982) can vary seasonally, even when egg production is constant. These recruitment fluctuations then generate the abundance modes which permit analysis of length-frequency data (Pauly 1984). The demersal fish fauna of the Mexican Pacific Ocean has been but poorly studied; most work has been carried out in the Gulf of California, and has been based on aspects of systematics (Walker 1960; Castro-Aguirre et al. 1970; van der Heiden et al. 1982; van der Heiden 1985; Thomson et al. 1987; van der Heiden and Findley 1988); commercial fishery (Chfvez and Ramos-Padilla 1974; Mathews et al. 1974; Arvizu-Martfnez 1987; Stromme and Saetersdal 1988; Acal and Arias 1990) and community structure (Bianchi 1991; Plascencia-Gonzflez 1993). Biological data for demersal species are scarce; a preliminary study was made on the growth of Synodus evermanni based on otolith growth patterns (Morales-Nin 1993), and a biological study on Caulolatilus affinis and C. princeps has also been carried out (Elorduy 1993). The present paper describes the growth of 24 demersal species caught off the northwestern and southern coasts of the Mexican Pacific Ocean, determined by length-frequency analysis. Growth rates in both areas and between species are discussed.
Materials and methods Data collection As part of an EU-sponsored research project ("Requirements for the restructuring of Mexican Pacific demersal fisheries"), eight research cruises (CEEMEX-P1 to CEEMEX-P8) were carried out by the R.V. "El Puma"; five in the Sinaloa-Nayarit area and three in the Gulf of Tehuantepec (Fig. 1) from 1989 to 1992. During each cruise, the demersal macrofauna was sampled with a C-80 shrimp trawl net. The fishes from each catch were identified and measured, and their total lengths were rounded down to the nearest 1 cm. The length-fre-
212 Fig. 1 Study areas in Mexican Pacific Ocean. A Sinaloa-Nayarit area; B Gulf of Tehuantepec ( 9 stations sampled in CEEMEX research cruises)
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quency distribution for each species was determined for each cruise. Growth parameters were calculated for each species on each cruise by means of a length-frequency analysis that covered a large size range and included enough fishes to produce clear modes. The number of fishes measured and their length ranges for each cruise are shown in Table 1. The length-frequency for each species and area was analyzed by the ELEFAN method (Gayanilo et a1.1988).
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Length-frequency analysis Variations in the frequency of age-classes over time can be determined by direct observations (Petersen 1891), or by using a computerized method developed from the Hasselblad (1966) technique for separation of modal length-classes into a length frequency matrix (MacDonald and Pitcher 1979; Schnute and Fournier 1980). Pauly and David (1981) analysed such time sequences by assuming that
213 Table 1 Length ranges (cm) and numbers of species sampled on each CEEMEX cruise. Cruises CEEMEX P4, P5 and P7 were in Gulf of Tehuantepec, remainder were off Sinaloa-Nayarit coast Species
P1
Albula vulpes
1-19 31
Bagre panamensis
P2
P3
P5
6-37 22
6-40 164
6-12 332
6-12 160
P6
P7
P8
10-36 61
Balistes polylepis Porychthys analis
P4
5-39 47
8-19 252
Engoyophrys sanctilaurenti
4-15 483
Monolene asaedai Brotuloides cf. enmales
5-13 178 5-22 580
Selene peruviana
5-21 783 12-21 81
Diapte rus peruvianus Diapterus aureolus
8-14
6-13
Pseudopenaeus grandisquamis
76 7-17 48
254 7-24 936
7-21 53
7-19 70 7-29 79
Lutjanus peru Ciclopsetta querna Citharichthys platophrys
6-29 57 4-15 2126
4-35 704
8-12 87
Syacium latifrons Syacium ovale
9-18 79
9-20 50 12-29 81 18-43 65
Pomadasys axillaris
5-17 311 6-17 74 16-70 16
Pomadasys nitidus Epinephelus analogus Diplectrum macropoma
6-24 603
9-24 67 10-29 842
Synodus scituliceps Prionotus stephanophrys
6-25 579 6-26 355
6-18 208
7-18
Diplectrum labarum Synodus evermanni
5-55 215 14-20 178 5-12 765
5-23 358 9-16 50
7-19 215
7-24 635
4-24 464
8-28 373
the mode of each age-class is best described by a von Bertalanffy growth curve. A seasonal growth curve (Pauly 1979) was used for growth determination: Lr=L=(1-eK(t-t~ + CK/au sin(2u[t-td)), (1) where t=time, ts=the commencement of variations in sinusoidal growth with respect to t=0 [ts=WP+0.5, where WP=that point in winter at which minimum growth occurs (0
8-19 31
10-20 102 7-20 63 20-36 39
8-32 334 5-12 456
6-27 356
7-18 477 7-18 66
459 7-19 67 8-23 499 11-38 79 6-12 113
6-12 123
To estimate L~, Wetherall et al. (1987) used a regression method derived from the formula of Beverton and Holt (1957), whereby Z=the total instantaneous mortality coefficient, L~ and K are von B ertalanffy growth parameters, and Lm=mean length in a random sample of fish above length L c, Lc=the length selected; it is assumed that fish larger than this have been fully recruited to the fishery. The mean length offish greater than L C(i. e., Lm) is a linear relationship between L~ and Z/K:
Lm=L~[{ (Z/K)/(Z/IO+ 1) }(L~-Lc) ].
(2)
After estimating L~ for each species by this method, a yon Bertalanffy growth curve was fitted to the length frequencies using the ELEFAN I procedure (Pauly and David 1981). By restructuring the frequencies, this procedure aids the identification of cohort peaks independent of their height or assumed shape, The frequency Fr of each
214 length-class i (i=1... n) is divided by the moving average (MAi) over five length-classes. The values of FAi=(Fi/MAi) identify peaks (FAI>_ 1) and troughs (FAi,< 1). The average adjusted frequency value, FA, is then computed and the final transformation is made according to the equation: F~'=FAJFA-1. (3) In a set of restructured length-frequency samples (ns=number of samples), a number of peaks (np) lie within each ns sample. Each peak (F/') is presumed to represent a distinct age-class, and any growth curve passing through a peak would intersect only one of the lengthclasses constituting that peak. Thus, the maximum sum of positivepoint values that can be accumulated by a growth curve equals the sum of all np peaks in all ns samples; this is the available sum of peaks (ASP). Any growth curve fitted to a restructured length-frequency matrix will intersect a number of points within the matrix. Summing the restructured frequency values corresponding to these points gives the explained sum of peaks (ESP). The fit of a growth curve passing through a restructured lengthfrequency data matrix is determined by the number of intersected peaks in relation to the total number of available peaks. The value obtained for the goodness-of-fit index, Rn=ESP/ASP (0
R es u l t s and discussion
This study was not centred on commercially exploited fish species, since only a few littoral species are exploited and these were rare in the research-cruise hauls. It was thus considered appropriate to gather data for as many species as possible. All species with sufficiently representative length-frequency data have been analyzed, even if encountered only during one cruise. The growth parameters L~ and K were calculated for 24 species (Table 2).
Fig. 2 Growth of all fish species studied, expressed as loga rithmic relationship between asymptotic length (L~cm) and von Bertalanffy growth c o e f f i cient (K yr- 1). Species codes are explained in Table 2
Asymptotic length L~ and the growth coefficient K were correlated in order to study trends between species. Pauly (1979) and Munro and Pauly (1983) used the growth-performance index, ~= 21og(L~) +log(K), as a taxon-specific index of growth performance. Manooch (1987) later employed the growth-performance index to graphically summarize the growth data of tropical lutjanids and serranids. Using the same criteria, log (K) was plotted against log(L~) for all the species studied. The resulting plot (Fig. 2) was linear with a negative slope, its y-intercept provides an index of growth performance. The regression line (Fig. 2) is log(K)=0.6319-0.69025 log(L~). Standard error estimates for the slope and intercept are 0.1512 and 0.156, respectively, and the correlation between the two parameters is relatively low (r2=0.4545). A clear inverse relationship existed between theoretical m a x i m u m size (L~) and the von Bertalanffy growth coefficient (K). The plot shows a tendency towards a linear arrangement of the data points representing the various species, with slow-growing fishes at the bottom right and the fast-growing at the top left. The Lutj anidae and S erranidae, long-lived species which attain large sizes, are clearly differentiated in the plot. Selene peruviana is the fastest-growing species, while the majority of the species display intermediate values. In those cases where data were sufficient to calculate seasonal growth (Eq. 1), most species exhibited similar W P values, indicating minimum growth in spring. C values were moderate, reflecting seasonality in this tropical ecosystem (Table 2). For species common to both study areas, growth rates were greater in the south (Gulf of Tehuantepec) than in the north (Sinaloa-Nayarit). The one exception was Albula vulpes, which displayed the same growth rates in both areas (Table 2). The Mexican Pacific Ocean is characterized by complex current patterns. The surface currents off the Mexican and Central American coasts are dominated by two main systems: the California Current and the North Equa-
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215 Table 2 Asymptotic length (L=), Von Bertalanffy growth coefficient (K), seasonal growth oscillation (C) and minimum point of growth (WP) for species studied, species codes are used in Fig. 2 (Sin-Nay Sinaloa-Nayarit area; GT Gulf of Tehuantepec) Species
Species Code L=(cm)
Kyr 1
Albulidae Albula vulpes
AV
47.3
0.275
Sin-Nay
Ariidae Bagre panamensis
BP
44.1
0.37
Sin-Nay
BPO
37
0.49
PA
25.2
0.38
Sin-Nay
ES MA MA
21 17 13.4
0.56 0.31 0.64
Sin-Nay Sin-Nay GT
BE
24.2
0.45
Sin-Nay
SP
21
0.95
DP DA
21 13.6
0.65 0.57
PG PG
25 20.3
0.5 0.61
LP
61.4
0.14
GT
CQ CP SL SO
29.3 32 19.1 24.1
0.35 0.24 0.86 0.72
Sin-Nay Sin-Nay GT Sin-Nay
PAX PAX PN
29.2 21.1 17.9
0.42 0.51 0.36
Sin-Nay GT GT
EA DM DL DL
97.3 17.8 24.2 18.5
0.12 0.61 0.41 0.6
Sygnodontidae Synodus evermanni Synodus scituliceps
SE SS
24.5 39
Triglidae Prionotus stephanophrys
PS
28
Balistidae Balistes polylepis Batrachoididae Porychthys analis Bothidae Engyophrys sanctilaurenti Monolene assaedai Brotulidae Brotuloides cf enmelas Carangidae Selene peruviana Gerridae Diapterus peruvianus Diapterus aureolus Mullidae Pseudopenaeus grandisquamis Lutjanidae Lutjanus peru Paralichthydae Ciclopsetta querna Citharichthys platophrys Syacium latifrons Syaeium ovale Pomadasyidae Pomadasys axilIaris Pomadasys nitidus Serranidae Epinephelus analogus Diplectrum macropoma Diplectrum labarum
torial Current. The California Current, which originates in the Arctic, carries water southward along the coasts of California and Baja California. This water mass is easily identified by its low salinity, low temperature and high dissolved oxygen content. The California Current meets the North Equatorial Current (which flows from east to west at maximum velocities slightly in excess of 1 km/h) near Cabo San Lucas and Cabo Corrientes (at the mouth of the Gulf of California). In this area, salinity and temperature gradients are very high. Although the principal oceanic circulation is driven by these two currents, there are local and seasonal current patterns that affect the northwest coast of Baja California and
C
0.55
0.7
WP
0.2
0.3
Area
GT
Sin-Nay Sin-Nay Sin-Nay
0.2 0.2
0.5 0.5
Sin-Nay GT
GT Sin-Nay Sin-Nay GT
0.2 0.2
0.5 0.3
0.59 0.75
0.5
0.2
Sin-Nay GT
0.47
0.55
0.4
Sin-Nay
the gulfs of California and Tehuantepec. In these areas, water flows southeast during winter and northwest during summer. Between February and April there is a strong southwest current of 0.54 kin/h, and between June and August a northwest flow of 0.72 km/h. The southeast Central American coast is strongly affected by winds from both the Pacific and the Atlantic oceans. Winds blowing from the Atlantic are notable during the dry season (NovemberApril) and in summer. The winds and the resulting upwelling waters decrease water temperatures by 2 to 6 C ~ lower than in any other Central American region (Blackburn 1962, 1966; Wyrtki 1966, 1967; Fiedler 1992). This upwelling, which increases productivity, food availability
216 arid o x y g e n content, could e x p l a i n the more rapid growth observed in fishes in the south of the study area. Similarly, seasonal changes in oceanographic conditions, by directly affecting metabolic d e m a n d s ( m a i n l y through variations in temperature and o x y g e n content) and indirectly p r o v i d i n g more food, could be linked to seasonal variations in growth. Data on age and growth rates are f u n d a m e n t a l requirements for both studies on fish b i o l o g y and for the setting up of m a n a g e m e n t policies for p r e v e n t i n g overexploitation of fishery resources. L e n g t h - f r e q u e n c y analysis of tropical fishes has some s h o r t c o m i n g s arising from protracted r e c r u i t m e n t periods and m a j o r overlaps of adjacent ageclasses ( M a n o o c h 1987). Nevertheless, such analysis permits the e s t i m a t i o n of growth parameters when other approaches are not possible. D e m e r s a l fishes in the M e x i c a n Pacific O c e a n are h e a v i l y exploited as a by-catch of the shrimp fishery (Acal and Arias 1990), and could b e c o m e the basis for a direct fishery. I n f o r m a t i o n on their b i o l o g y is therefore needed to provide the basis for future m a n a g e m e n t of stocks. The diversity of demersal fish species is impressive, 235 species were identified during the C E E M E X cruises (van der H e i d e n personal c o m m u n i c a tion). H o w e v e r length-based methods are rapid and can provide basic data such as those presented in this paper. In future studies, age data from otolith interpretation could be used to c o m p l e m e n t l e n g t h - f r e q u e n c y analysis and thus i m p r o v e the accuracy of growth determinations. Acknowledgements I would like to thank the crew and participants in the CEEMEX cruises, particularly the cruise leader Dr. A. van der Heiden, for their cooperation. This research was sponsored by the DG XII of the EU (Contracts TS2.0213.E and CI1.0431.E) and by the Spanish DGCICYT (Ref. CE89-0006). B. Lynas translated the Spanish text.
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