Estuarine p production of resident and nursery fish species: conditioning by drought events? Dolbeth M*1, Martinho F1, Viegas I1, Cabral H2, Pardal MA1 IMAR - Institute of Marine Research IO – Institute of Oceanography *
[email protected]
Major Aim Production of the resident and marine juvenile fish species of the Mondego estuary (70% of all fish community)
1)
productive potential of the estuary for the fish resources (and other consumers)
2)
production potential for exportation by the marine juveniles to the coastal stocks
3)
how natural climate stress influence the production estimates i
Mondego estuary Central PORTUGAL Warm temperate region Small estuary: 10 km long x 2-3 k cross (widest km ( id part) 2 arms of distinct hydrologic characteristics
North Arm •
Deeper p ((4-10 m during g high g tide,, tidal range g 1-3 m))
•
Mercantile harbour of Figueira Foz city and main navigation channel
•
Constant dredging and shipping, as main impacts
Strongly modified sub-system of the Mondego estuary
South Arm •
2-4 m during high tide, tidal range 1-3 m
•
Large areas of intertidal flats (about 75% of total area)
- Almost coastal lagoon g - upstream p areas were silted up p until 1998 - Water circulation: tides, freshwater input from the Pranto river - Severe eutrophication in mid 80’s - 1998: implementation of a restoration plan - system gradually recovers
Sampling Beam trawl Ebbing tide spring tides, night 3 hauls (10 to 15 15‘ per station) 3 years: June 03 – May 06 Monthly
M – Mouth, 8.7 m deep, constant dredging N1 – North arm, 5.5 ± 0.5 m deep, regular freshwater flow N2 – North arm, 4.5 ± 0.3 m deep, permanent freshwater flow (Mondego river) S1 – South arm, 2.3 ± 0.4 m deep, upstream the Zostera noltii bed S2 – South arm, 2.4 ± 1.0 m deep, near Pranto river sluices
Data Analysis ¾ Resident species: Pomatoschistus minutus, Pomatoschistus microps ¾ “N “Nursery”” species: i Di Dicentrarchus t h labrax, l b Platichthys Pl ti hth flesus, fl Solea solea Population structure defined by tracking recognizable cohorts from the successive sampling dates: - ANAMOD and FiSAT software After recognition of the cohorts, the annual production was estimated by the cohort increment summation method (Winberg 1971): T −1
Pcn =
⎛ N t + N t +1 ⎞ ⎟ × (w t +1 − w t ) ⎜ 2 ⎠ t =0 ⎝
∑
(Negative production values were not accounted for the overall production estimates)
Environmental conditions Precipitation and water runoff
D Drought ht
Low fresh wate r runof f
Extreme drought
Low freshwater runoff
Lower annual precipitation values compared to the 1940-1997 mean; Lowest values in 2005: consequent severe reduction of water runoff
Environmental conditions Salinity Drought
Low fresh wate r runof f
Extreme drought
Low freshwater runoff
Higher salinity in south arm and estuary mouth Extreme drought year: higher salinity incursion incursion, abnormal high salinity in the most upstream area – N2
Environmental conditions Mean water temperature
Water temperature with typical variation found in temperate regions;
Higher g temperatures p in July y 2003 and July y 2005,, especially p y in the most upstream sampling stations S2 and N2 (24ºC to 26ºC night temperature)
Resident species production P. minutus and P. microps Annual production
• Higher production for P. minutus
• Drought: clear decrease in 2004/05, 2005/06 for P. minutus • Similar production for P. P microps along the 3-year study period
Monthly production
Nursery species production D. labrax, S. solea and P. flesus Annual production
• D. labrax with higher production • Drought: D. D labrax and P. P flesus decrease production
Monthly production
Exportation of nursery species D. labrax
Monthly production of selected time periods D. labrax
10 months 4 – 14 cm S. solea S. solea
10 months 6 – 20 cm P. flesus
P. flesus
9 months 7 – 14 cm
Conclusions Production decreased in the drought g y year ( (2005), ), especially evident for D. labrax, P. minutus and P. flesus A significant g reduction o (( 15 to o 45%) ) was also o concluded o for the potential production to be exported for coastal areas by the nursery species in the drought conditions Estuaries are exposed to severe of anthropogenic and inherent natural stress, being difficult to distinguish between the two sources of impacts impacts, yet yet…
Conclusions salinity variations low l freshwater f h t discharges di h temperature variations
Probable major driving forces acting in the recruitment it t success and d population development of species
¾ Li Limiting iti effect ff t off hi high h ttemperatures t and d salinity li it variations i ti on eggs and larvae development ¾ Decrease in river discharge: potentially lower primary production and the chemical cues for by larvae of marine species in coastal areas ¾ Higher salinity incursion in the estuary increased the piscivorous marine adventitious species: increase of predation
