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Procedure for modelling construction scenarios

PREHAB calculated the rate at which critical fish recruitment habitats are exploited by combining the estimated rates of construction with modelled maps of the distribution of fish habitats. Based on aerial photographs since the 1960’s, we estimated shoreline development/construction rates. The distribution of spawning habitats for the dominating top predatory fish, perch (Perca fluviatilis), was based on predictions from species distribution models.

 

 

 

 






 

 

Map of study area in Stockholm archipelago, including 5 subareas.

 


I. Estimating shoreline construction development rates
Aerial photographs from 1960, 1986 and 1999 were collated in five subareas of the Stockholm archipelago (see map). Based on the number of jetties and marinas recorded along the shoreline, an index of construction was developed for all areas and years. A neighbourhood analysis was utilized to calculate the frequency distribution of constructed objects (jetties and marinas) within 100 m radius. The resulting construction index values were classified from 1 to 5, where classes 3-5 were considered as constructed to such an extent that they have the potential to affect fish habitats (Table 1). Shorelines within urban areas as of 1999 was excluded from the analysis.

 

 

 

 

Table 1.
Index classes based on number of observed jetties/100 m (Freq) and Category (affect on fish habitats).
Classes 3-5 are considered to have a negative affect on fish habitas.

 

 

Two scenarios were adopted based on the three years and five subareas. The first scenario was based on spatial differences among the five areas and utilised the average and highest trends observed. The second scenario was based on temporal differences and utilised annual rates of change by assuming linear trends between 1960 and 1999 and between 1986 and 1999, where the later time period had a higher construction rate (Table 2).

Table 2

 

Table 2
Annual rate of change scenarios given observed temporal and spatial trends. Average and high rate of change scenarios are based on spatial differences among the subareas and are calculated as the amount of shoreline in construction class 3-5 per year for the two time periods.

 

Annual rate of change shoreline construction rateFig 2. Annual rate of change in amount of shoreline per construction class between a) 1960-1989 and b) between 1986-1999. Red line signifies the highest trend scenario and black line the average rate of change scenario.
 

II. Modelling fish habitat distribution
Should be mentioned here, right? With a link to the Mapping-part of web-resource?


III. Estimating shoreline construction overlap with fish habitats First, we calculated the percentage of predicted fish habitats within constructed parts of the shoreline. To incorporate the uncertainty of "effect distances", this was done for 100, 200 and 500 m distance from the construction.

We then compared these figures (=the percentage of predicted habitats?) with the percentage of the shoreline that was constructed in general (to got the quota below?).

This quota yielded a conversion factor (="target factor"?) specifying to what extent fish recruitment habitats is targeted by jetties and other constructions.


IV Calculating the rate of fish-recruitment-habitat-exploitation

Finally, we combined the “target factor” with the (construction?)rate of change scenarios to obtain expected yearly exploitation rates of fish habitats.
 


Results/conclusions - this part I have not yet worked with!

Yearly percent loss of fish habitats at different levels of shoreline constructionFigure
Yearly per cent loss of perch (Perca fluviatilis) recruitment habitats at different levels of shoreline construction. Number of jetties per construction class is given in table 1. Error bars show standard deviation depending on at which distance from the shore recruitment habitats are affected (100, 200 and 500 m).

 

  • Rate of change in the period 1986-1999 was higher than in 1960-1986 (Figure 2, Table 2). The amount of shoreline with a clear to heavy construction (class 3-5) has on average increased from 3.6 % in the 1960’s to 13 % in 1999 and from 5.1 % to 25 % in the most heavily constructed area.
     
  • Shoreline construction was concentrated to important fish reproduction habitats. For each percent of shoreline constructed, 2.9 % (±0.6 SD) of available fish habitats were on average affected.
     
  • On average about 1 % of available fish recruitment habitats was estimated to be lost annually between 1986 and 1999, along shore lines classified as having clear indication of construction or higher (Figure results). In comparison, the high rate area had an annual loss of 1.6 %. Also, the high rate area was more dependent on class 3 (i.e. clear indication of constructed shoreline) than the average subarea.
     
  • Over a longer time period, the 1960-1999 scenario, similar trends were observed. There was a slight increase in the amount of shoreline classified as very high indication of construction (class 5) – även om detta med största sannolikhet inte är en significant skillnad kan det vara värt att lyfta till webresursen?
    - Någon mer relevant slutsats från den figuren vi vill lyfta till webresursen?
     
  • At current development rates untouched shores may be lost in 150 years (Kindström 2006). Critically, our results indicate that recruitment habitats for perch may be fully exploited by boating activities already in 100 years (Table results). Observed rate of construction are even higher in some areas, suggesting that available perch habitats may be completely exploited already in 60+ years.

 

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