origina! scientific paper	 UDK 597.5(262.3-17) 
SPAWNING OF THE ANCHOVY , ENGRAULIS ENCRAStCOLUS (L) , IN THE NORTHERN ADRIATIC SEA IN 1989, THE YEAR O F INTENSIVE BLOOMS 
Jakov DULČiČ 
PhD., fisheries biologist, institute of Oceanography and Fisheries - Split, 21000 Split, Šei. I. Meštroviča 63, CR O dr., ribiški bioiog, !OR, 21000 Split, Set. i. Meštrovida 63, CR O 
ABSTRACT 
The main spawning area of the Adriatic anchovy (Engraulis encrasicolus) is the shallow Northern Adriatic. In 1989, an unusually low anchovy egg production, a considerable mortality of larvae, and an unusual location of spawning centers in the limited areas were recorded in the Northern Adriatic. Since the major part of the Northern Adriatic was covered by the phytoplankton and benthic diatoms blooms, gelatinous aggregates and "marine snow" during the peak of the spawning season, it is speculated that they caused the observed anomalies in the reproduc­tion of this fish. 
Key words: anchovy, spawning, Northern Adriatic, blooms 
Ključne besede: inčun, drstenje, Severni Jadran, cvetenje 
INTRODUCTION 	The severe bloom events began to decrease in 1990. Since these two phenomena coincided both spatially 
Long-term estimates of the anchovy, Engraulis en-and temporally, the spawning of the anchovy in the crasicolus, biomass in the Adriatic showed a continuous Noithern Adriatic during the 1989 spawning season was decrease since 1978 (Regner etal., 1985; Quick, 1993; analyzed in order to determine whether a connection DuiCid & Cetink, 1993). The anchovy stock almost between the blooms and anchovy reproduction exists. collapsed during the years 1986-1989, Since the sardine stock increased in the same period (Vucetk & Alegria-MATERIAL AN D METHODS Hernandez, 1987), this phenomenon couid not be at­tributed to overfishing. Curing the same period, exce-Plankton material was collected at 14 stations in the sive summer blooms of phytoplankton and benthic dia-Northern Adriatic during R/V three cruises carried out in toms became regular events in the Adriatic Sea. The June 13-14, July 6-7 and July 24-25 (R/V "Vila Velebita", 
surface affected by the blooms (Marchetti et al., 1988; Nansen plankton net, diameter 80 cm, vertical tow 0.5 Todini & Bizzari, 1988; Filipk, 1990; Deggobis et al, m/s), and at 20 stations in August 15-18 (R/V "Vila 1991), large quantities of gelatinous (mucilaginous) Velebita" and "Bios", Nansen net and Bongo-20 plank-material (Deggobis et al., 1991; Rinaldt et al., 1990; ton net, two cylindres of 20 cm diameter, oblique tow, Cabrini et al., 1992; Deggobis et al., 1995) and "marine 
1.5 to 2 knots). Both nets were of 250 |im meshes. At snow" (including flocks, strings and small clouds) each station, data on temperature and salinity from the (Fonda-Umani etal., 1989; Fanuko & Turk, 1990; Deg­surface to the bottom were collected by CTD probe at 1 gobis et al., 1991; Deggobis et al., 1995) was increasing m intervals. 
from year to year, particularly in the shallow Northern The anchovy plankton i c stages were separated from Adriatic and along the Italian coast up to the peninsula the samples, eggs were classified into five developmen­of Gargano, corresponding precisely to the spawning tal stages, yolk-sac larvae into three length groups, and season and the main reproductive areas of the anchovy. 
larvae into length groups of 2 mm. instantaneous mor­
;••<<•,• DUlCC : SPAWNING C f TH i ANCHOVY, SNCSAUU S ENCRASICOLUS<U, IN THE NORTHERN ADRIATIC SEA IN 1989, ..., 51-5') 
tality rates of eggs, yolk-sac larvae and larvae were es­timated, and the quantity of anchovy eggs was ex­pressed as the number of eggs produced per 1m 2/day. For details on egg production estimates see Regner (1985); Regner et at, (1985), as well as Piccinetti et a!. (1982); Regner & Duleid (1990) provide estimates for mortality of larval stages. 

RESULTS 
Intensive algal blooms, gelatinous aggregates and "marine snow" were recorded in Northern Adriatic in June-August 1989. In June the blooms were limited to the coastal waters along the Italian coast, while in July and August they spread over all the Northern Adriatic, with the exception of a 10-15 mile wide zone along the west istrian coast. This zone was under the influence of the geostrophic current which brings the Mediterranean water of lower temperatures and higher salinity through the Central and Southern Adriatic. The surface of all the other areas of Northern Adriatic was covered with dense patches of mucous matter released by pelagic diatoms; echo sounders showed that these patches were dense and randomly distributed from the bottom to the sea surface. 
The estimates of mean daily production of anchovy eggs over the surveyed area was considerably low in all the surveys (Table 1). 
Month  No. eggs/m2/day  95% confidence limit  
lower  upper  
june  2.5  1.79  3.21  
July (early)  1.5  1.09  1.91  
July (late)  5.5  3.73  19.3  
August  47.6  32.91  99.91  

Table 1: The estimates of mean daily production of an­chovy eggs in the Northern Adriatic (1989). 
Tabela 1: Ocenjene srednje vrednosti dnevne produk­cije iniunovih iker v severnem Jadranu (1989). 

As far as the spatial distribution is concerned, in June, when the blooming was not yet widespread, two centers of spawning, although of very low intensity of only 3 eggs/mVday, were observed. One was situated in the northwestern part of the surveyed area, in the waters influenced by the river Po inflow, while the other one was found about 6 miles off the Istrian coast {Fig. 1). !n July, during the heavy blooms, spawning areas of the same intensity were found along the istrian coast (Fig. 2). In August, one center of relative intensive spawning (100 or more eggs/W/day) was found in an area 10 to 20 miles off the Istrian coast {Fig. 3). This center was situated at the edge of the frontal zone where Northern Adriatic waters and the geostrophic current collide. 
This indicates that anchovy could not spawn in eu­trophic waters of central and western parts of Northern Adriatic, which are their traditional spawning areas, probably because these parts were under the strong in­fluence of blooms. They were apparently forced to spawn either in the narrow and relatively oligotrophic zone along the coast of istrian peninsula, or in the fron­tal zone where the water was still relatively "clean". 
The instantaneous mortality rates of anchovy plank­
tonic stages were estimated (Table 2).  
Stage  Mortality rate  Standard error  F  P<  
Eggs and yolk-sac larvae -0.4849  0.0228  452.16  0.001  
Larvae  -0.5181  0.1393  13.83  0.1  

Table 2. The instantaneous mortality rates of anchovy planktonic stages in Northern Adriatic (1989). Tabela 2; Hipne stopnje mortalitete planktonskib stadi­jeviniuna v severnem Jadranu (1989). 
It should be emphasized that for the first time since mortality of anchovy planktonic stages has been studied (20 years), the mortality rate of larvae was higher than that of eggs and yolk-sac larvae. At the same time, the fact that no larvae older than 12 days {7 days after the complete yolk-sac resorption) have been found (Fig. 4) indicates that conditions for their survival were unusu­ally unfavourable in the Northern Adriatic during the 1989 spawning season. 
Fig. 1: Anchovy egg distribution (N/m /day) on June 13­
14, 1989. 
Slika 1: Razširjenost inčunovih jajc (N/m/dan) 13. in 

14. junija 1989. 

lakov PUI.ČIČ: SPAWNING OF THE ANCHOVY, ENCRAULIS ENCRASICOLUS iU, IN THE NORTHERN ADRIATIC SEA IN 1989,51-5< ! 
Fig. 2: Anchovy egg distribution (N/m /day) on fuiy 24­25, 1989, 
Slika 2; Razširjenost inčunovih jajc (N/m/dan) 24. in 25. 
junija 1989. 


DISCUSSION 

The anchovy egg production during the investigated period from June to August 1989 was the lowest ever re­corded in the Northern Adriatic (Varangolo, 1967; Štirn, 1969; Piccinetti ef at., 1982; Regner et a!., 1985). The spatial distribution of the spawning centers, particularly during the months (second part of June, July) of the most intensive bloom (Deggobis, 1989; Deggobis etai, 1995), indicates that the anchovy could not spawn in its main spawning area which, according to the above mentio­ned authors, is normally situated in the eutrophic waters of the central and western part of the Northern Adriatic. Rather, the fish were apparently forced to spawn in the limited areas of relatively "clean" waters, where the environmental conditions for its reproduction were less suitable. At the same time, the mortality rate of anchovy larvae was found to be considerably higher than the previously estimated rate in the same area and with the same methods applied (Piccinetti et at., 1982). This event, together with the lack of older larvae in all the samples collected, indicates that not only the conditions for spawning, but also the conditions affecting larval survival were unfavourable during the period of blooms. 
Since there is no direct evidence on the interrela­tionship between anchovy spawning and the blooms, no clear explanation can currently be given on how the blooms might affect anchovy reproduction. One hypo­thesis is that they change the chemical properties of the water as well as the quantitative composition of the plankton, which would in turn affect the trophic status of both adult fish and larvae. The blooms may perhaps even physically irritate the adult fish, while the patches of mucous matter can act as a trap for yolk-sac larvae and 
Fig. 3: Anchovy egg distribution (N/m day) in August 
15-18, 1989. 
Slika 3: Razširjenost inčunovib jajc (N/m/dan) od 15. 
do 18. avgusta 1989. 

larvae. As a matter of fact, several yolk-sac larvae and larvae collected with the plankton nets had obviously died prior to capture: they were clearly decomposed and enveloped in the mucous matter. Most probably all these factors act simultaneously. 
Since the regions covered by excessive blooms gradually spread during a long period of years, particu­larly over the principal spawning areas of the anchovy, it can be supposed that anchovy reproduction was seri 
6 —  
5 —  \ \s  
i, ~  
3 —  
o  
^  2 —  A  
•v,z  j  _  ^ •X  \  \  
cz  0 —  X  
-1 — -2 —  "' V Eggs and larvae Pastlarvae95 confidence limits \ VN \ n  \. \  
\  
C) t 2  i 4  1 6  1 8  I 10  ;  12  
Days  from  hatching  

Fig. 4: Estimated mortality rates of anchovy planktonic 
stages. 
Slika 4: Ocenjena mortaliteta planktonskih stadijev in­čuna. 

Jaksw DUlCKi : SPAWNING OF THE ANCHOVy. FNCRAUUS ENCRASICOLUS il.l IN THE NORTHERN ADRIATIC SEA IN 1989, ..., 51-54 
ously disturbed during this period due to gradual reduc­tion of their reproduction areas. Finally, when the blooms reached their maximum, the fish were forced to reproduce in the limited areas of relatively clean waters where they usually do not spawn intensively. Therefore, blooms, gelatinous aggregates and "marine snow" are potentially one of the main factors responsible for the decrease of the anchovy stock in the Adriatic. 

POVZETEK 
Glavno drstišče jadranskega inčuna Engraulis encrasicolus je plitvi severni del jadranskega morja. Leta 1989 tu ni bila ugotovljena le nenavadno nizka produkcija inčunovih iker; pač pa tudi precejšnja mortaliteta larv in nenavadna lokacija drstitvenih središč v omejenih območjih tega dela Jadrana. Upoštevaje dejstvo, da je bil severni Jadran na vrhuncu drstitvenega obdobja poln cvetočega fitoplanktona in bentonskih diatomej (kremenastih alg), želatinastih agregatov in "morskega snega", bi lahko sklepali, da so prav ti dejavniki povzročili opažene anomalije v 
reprodukciji jadranskega inčuna. 
REFERENCES 

Cabrini, M., Fonda-Umani, S., & Honsell G. 1992. 
Mucilaginous aggregates in the Gulf of Trieste {Northern Adriatic Sea): analysis of the phytoplankton communi­ties in the period June-August 1989. Sci. Total Enviro. Suppl., 557-568. Deggobis, D. 1989. Increased eutrophication in the northern Adriatic Sea. Second Acta Mar. Pollut. Bull., 
20: 452-457. 
Deggobis, D., Precali, R., ívanCté, I., FiiipiC, B., & Smodfaka N. 1991. Mogud mehamzmi stvaranja sluzavin nakupina u sjevernorn jadranu u razdoblju 1988-1990. Pomorski zbornik, 29: 337-354. 
Deggobis, D., Fonda-Umani, S., Franco, P., Malej, A., Precaii, R., & Smodiaka N. 1995. Changes in the northern Adriatic ecosystem and the hypertrophic ap­pearance of gelatinous aggregates. The Science of the Total Environment, 165:43-58. Dulék?, ). 1993. Stock assessment of the Adriatic an­chovy (Engraulis encrasicolus L.) using the egg surveys. Acta Ichthyologica et Piscatoria, 23 (1): 69-76. DuICi., J., Cetinid P. 1993. Estimate of spawning biomass of anchovy, Engraulis encrasicolus, in the east­ern part of Adriatic from 1989 to 1990 by means of egg surveys. Acta ichthyologica et Piscatoria, 23 (2): 67-76. Famiko, N., & Turk V. 1990. The oceanologic properties of the seawater in the Gulf of Trieste before and during "mare sporco" phenomenon {summer 1988). Boll. Oceanol. Teor. Appl., 8: 3-11. 
Fiiipic, B. 1990. "Cvjetanje mora" u sjevernorn jadranu u proljetno-ljetnom razdoblju 1988. godine. Acta Bot. Croat, 49: 53-61. 
Fonda-Umani, S., GhírardeJü, E., & Specchi M. 1989. 
Gli episodi di "mare sporco" nell'Adriático dal 1729 ai giorni nostri. Regione Autonoma Friuli-Venezia Giulia, Direzíone regíonaie dell'Ambiente, Trieste, 178 pp. 
Marchetti, R., Gaggino G.F., & Provini A. 1988. Red tides in Northwest Adriatic. MAP Tech. Rep,, 21: 133­
142. Piccinetfi, C., Regner S., & Speccbí M. 1982. Pre­liminary data on larval and postlarval mortality of an­chovy Engraulis encrasicolus (Linnaeus, 1758) in the Northern and Central Adriatic. Acta Adriat, 23 (1/2): 449-456. Regner, S. 1985. Ecology of planktonic stages of the anchovy, Engraulis encrasicolus {Linnaeus, 1758), in the central Adriatic. Acta Adriat., 26 (1), Series Monog­raphic, 1: 1-113. Regner, S., Piccinetti C v & Specchi M. 1985. Statistical analysis of the anchovy stock estimates from data obtained by egg surveys. FAO Fish. Rep., 345:169-184. Regner, S., & DuiCií J. 1990. Growth parameters of anchovy post larvae in the Adriatic estimated from oto­lith growth rings. BiljeSke-Notes, Instituí za ocean­ografiju i ribarstvo, Split, 76: 1-7. 
Rinaldi, A., Montanari, G., Ghetii, A., Ferrari, C.R., & Penna N. 1990. Presenza di materiale mucillaginoso neii'Adriático Nord-Occídentale negli anni 1988 e 1989. Dinamica del process! di formazione, di diffu­sione e di dispersione, Acqua-Aria, 7-8: 561-567. Stim, ). 1969. Pelagia! sevemega jadrana. Razprave-Dissertationes, 12 (2): 1-92. 
Todini, E., & Bizzari A. 1988. Eutrophication in the coastal area of the region Emilia Romagna. MAP Tech, Rep., 21: 143-152. Varangoio, S. 1967. Osservaziont sulla riproduzione dell' Engraulis encrasicolus L. (Acciuga) dell'Alto Adriático. Arch. Oceanogr. Limnol., 15 suppl.: 71-81, Vufetií, T., & Alegria-Hemandez V. 1987. Trends of annual catches or stock densities of some pelagic fishes in recent "Pelagia years" in the Adriatic. FAO Fish, Rep,, 
394: 113-136.